73 i- '\ f i rr/y Soaa^jses. I -^ 1^ -T^" ,^. '«i t^ ■,Y> _■ ON ^ ^ I ■■ ''-ij THE VARIATION OF SPECIES WITH ESPECIAL REFERENCE TO THE IN8ECTA; FOLLOWED BY AN INQUIRY INTO THE NATUEE OF GENERA BY T. VERNON WOLLASTON, M.A., F.L.S a No compound of this earthly ball Is like another, all in all." Tennyson LONDON: JOHN VAN VOORST, PATERNOSTER ROW. 1856. \ J 9 ♦ f I 1 i i I J- I \ i \ " I do not enter so far into the province of the logicians as to take notice of the dif- ference there is between the analytic and synthetic methods of coming at truth, or proving it ;— whether it is better to begin the disquisition from the subject, or from the attribute. If by the use of proper media anything can be showed to be, or not to be, 1 care not from what term the demonstration or argument takes its rise. Either way propositions may beget their like, and more truth be brought into the world."- Religion of Nature Delineatedy p. 45 (a. d. 1722 J % 4 T I , r PRINTED BY TAYLOR AND FRA>XIS, RKD LION COURT, FLEET STREET. ^ ^ ff- t I I A TO ^ CHARLES DAEWIN, Esq., M.A., V.P.E.S., I Whose researches, in various parts of the world, have added r SO much to our knowledge of Zoological geography. this short Treatise is dedicated I i K r I I 1 -> i -^-^ n "' > * > ^ t \ \ PHEFACE. To make a dry subject entertaining, is impossible , but to render it, at any rate, readable, has been my endeavour in the following pages. How far I have succeeded in the experiment, it is not for me to decide. It having been suggested, by several of my friends, that it might be desirable to bring together into a small compass some of the evidence on Insect variation (with reference to external disturb - m causes) which my researches in the Madeira Islands have supplied me with, I have been en- couraged to do so : and I have added numerous conclusions from other data also, which have from time to time fallen in my way, — so as to confer '4 w- i VI I on tlie volume a more practical eneral naturalist. for the One of my main objects, however, has been to call attention to the fact, that the Annulosa have not been hitherto sufficiently considered, in the g question animals and some few of arising out of the distribution of mts ; hoping that, by so doin [• British entomologists, who have not looked into this branch of their science, may be induced to enlist themselves in the cause of Insect geography. If such a result be broudit about ; or if I be fortunate enough to open for discussion any of the topics which have been touched upon, and so lead to a more perfect solution of the problems which I have attempted to explain, I shall con- sider myself more than repaid. V I I 10 Hereford Street, Park Lane, London, May lOtb, 1856. n II /• CONTENTS. IM CHAPTER I. Page Introductory Remarks 1 CHAPTER II. Fact of Variation 7 As a matter of experience 8 As probable from analogy 10 CHAPTER III. Causes of Variation 19 § 1. Climatal causes generally (whether dependent upon latitude or upon altitude) 23 § 2. Temporary heat or cold, of an unusual degree ... 42 § 3. Nature of the country, and of the soil 46 § 4. Isolation ; and exposure to a stormy atmosphere . 70 1 CHAPTER IV, Organs and Characters of Variation , . . .' 95 CHAPTER V. Geological Reflections Ill CHAPTER VI. The Generic Theory 157 4 CHAPTER VIL Conclusion 181 *:. i «* 4 4 I 1 m COEEIG-EIN'DUM. Page 9O5 for Pecterojms Maderensis read Pecieroims rostratus, s SPECIEIC VARIATION IN THE INSECTA. iq s [■■ j CHAPTER I. INTRODUCTORY REMARKS. A VERY small amount of information gained by the V student in the field of Nature is sufficient to kindle the 4 desire to increase it. The more we know^ the more we are anxious to know; though the less we seem to know. It is one of the distinctive privileges of the naturalist that he has to labour in a mine which is inexhaustible : I the deeper he digs beneath the surface^ the richer is the vein for excavation^ and the more interesting are the facts which he brings successively to light. Dive he ever so deep^ Truths ^*^ at the bottom of the well/^ is assuredly present^ under some form or other^ to reward him stiU ; nor will she even for once elude his grasp^ provided he be content to receive her as she is^ instead of endeavouring to mould her to his preconceived ideas B If V 2 of what she onglit to be. In these times of patient re- search^ when the microscope is disclosing^ day by day^ fresh wonders to onr view^ and new lines of speculation from commoner questions -b kable that many to the members remained compai 3 of them ever he cussed at all^ except in a desultory manner and with insufficient data to reason from. Foremost amongst these^ numerous problems affecting the distinction be- tween '' varieties '^ and '' species '' (as usually accepted) especially dom Annulose less easy^ a priori ^ to pronounce upon. naturalist from the obscurer more philosophical inquirer), can have scarcely failed to re- mark from external agencies to which they have true m. vestigation of the circumstances on which such varia- tions do manifestly in a great measure denend, as though degr much theory. In the following pages I purpose, inter alia, to throw out a few general hints ; first, on the fact of aber- f } r^ a i t ! I L I I 3 mere matter of experience ; and^ secondly^ on some of the causes to whicli the physiologist would^ in many instances^ endeavour to refer it. ^ The former of these considerations (namely, the fact of specific instability as ordinarily noticed) nobody will he inclined to dispute : and yet it is abundantly evident that it cannot be taken into account, at any rate satis- factorily, without involving the latter also,— it being scarcely possible to attach the proper value to an effect without first investigating its cause. The importance of assigning its legitimate weight (and that only) to a variety, is perhaps the most difiicult task which the natural historian has to accomplish ; since on it depends the acknowledgment of the specific identity of one obj ect with another, — whilst, to draw the line of separa- tion between varieties and species is indeed a Gordian knot which generations have proved inadequate to untie. Now it is not the object of this pubHcation to attempt to throw positively new light upon a subject which has ever been one of the main stumbling-blocks in the lower sciences, and which is perhaps destined to be so to the end ; still less would I wish to imply that the causes of variation are altogether overlooked in these days of accurate inquiry,— when thousands are accumulating data, in all parts of Europe, destined to be wielded by the master's hand whensoever the harvest-time shall have arrived : but I do, nevertheless, beheve that there iwme: tendency, esneciaUv m perma b3 "( I L^^Li r :( / \ 4 nent) as a specific one ; and hence I gather the informa- tion that a reviewal of our first principles is occasionally necessary^ if we would not restrict (however gradual and imperceptibly) that legitimate freedom which Nature im pose laws of limitation in one department which we do r not admit to be coercive in another. Perhaps, however, before entering on the subject- matter of this treatise, my definition of the terms 'Variety/'— so far at least as such is ''^ species ^^ and ^ practicable, — will be expected of me. I may state, there- fore, that I consider the former to involve that ideal re- lationship amongst all its members which the descent i^ from a common parent can alone convey : whilst the iMter should be restricted, unless I am mistaken, to r those various aberrations from their peculiar type which are sufficiently constant and isolated in their general character to appear^ at first sight, to be distinct from it. The first of these enunciations, it Avill be perceived, takes for granted the acceptance of a dogma which I am fdly aware is open to much controversy and doubt, — namely, that of ""^ specific centres of creation.i^„ With- out, therefore, examining the~ evidences"' of that theory which would be out of place in these pages (and which has been so ably done already by the late Professor Edward Forbes), I would merely suggest that the admission of it is almost necessary, in order to convey to our minds any definite notion of the word " species " at all : and that, hence, whilst I would not wish to reject the hypothesis 1 / i J - w 1 5 as involving an absurdity (which I believe to be the exact opposite of the truth)^ I would^ in the present our postulate, assumed to >/ than as a problem capable of satisfactory demonstration. The second of the above definitions may likewise comm heard it asserted that everything is to be regarded as a ^^ variety ^^ which has wandered in the smallest degree from its normal state. Now this I contend is essentially an error ; for a "Variet y/ ^ to be tech nically such, must ■/ and to ■ \ moreover (which, although rarer than the variety itself, must nevertheless exist) to connect it with its parent stocks, its condition is such that it might be registered as speci-1 fically distinct therefrom. Thus, to take an. example for illustration, there are many darkly coloured insects which, as every entomologist knows, vary, by slow and regular gradations, into a pallid hue, almost white. It also most frequently happens, in such instances, that the eoctreme aberration is of more common sometimes occurrence than the intermediate ones. Here then is ; a case in point : there is but a single variety involved, namely a pale one, — the gradually progressive shades which imperceptibly affiliate it with its type not being regarded in themselves as ^^ varieties ^^ at all. If this indeed were not so, then would our position be far from pleasant, since we should be compelled to record, as a tl lilt i I I ill ( 6 variety^ every could \ possibly be found between the outer limits, — seeing that ■in- (mcreasmg, as tJiey did, m an even ratio) no one could be tabulated in preference to another. This however is an example in which the rate of altera- tion (so far as colour is concerned) is equal ; and one therefore in which the extreme end of the series can be alone singled out as the aberration to be specially noticed. It sometimes occurs that, between the two extremes^ there are several nuclei, or centres of radiation, to which the name of varieties may be legitimately applied,- asmuch as they may possess a series of characters which do not, all, in combination, progress evenly ; and which consequently stand out as it were, to a certain extent isolated, from the remainder. As a corollary arising out of these remarks, it would seem to follow that even small dijfferences should be re- garded as specific ones so long as the intermediate links have not been detected which may enable us to refer them to their nearest types. In a general sense, I beheve that it would be proper to do so : nevertheless there are instances, the results, for example, of isolation in which abrupt modifications may be a priori looked for ; and in which our judgment must be regulated by our knowledge of the local circumstances which may be reasonably presumed to have had some influence in pro- ducing them. The consideration of these, however and other kindred questions, must be deferred to a subse- quent chapter of this work. t I f mi' m i! t 7 i|*t V I CHAPTEE II FACT OF VARIATION. \\t (• I f It is scarcely possible to survey the members of the external world around us without being struck Avith the instability with which everything is impressed. The very shadows^ as they pass^ leave a moral lesson behind them on the mountain-slope^ which the student of Nature would do well to contemplate. Whatever be our preconceived ideas of the ^^ immutability of the uni- verse^^^ from first to last the same truth is re-echoed to our mind^ — that here all is change. Organic and in- organic matter are alike subjected to renovation and decay ; and^ dependent on that general law^ variability within specific limits would seem to be an almost neces- sary consequence. In the animal and vegetable king- doms^ this principle of fluctuation is peculiarly apparent ; and not more surely do the winds of heaven ruffle the forests over which they rage^ than does the ebb and flow r which is perpetually going on amongst created things mar their boasted constancy. The fact of aberration^ to which we would briefly r aUude in this chapter^ requires but little comment ; it is patent a priori. As a matter of experience^ every ob- server who has spent a week in the field of Nature « w l)i 111 I !| ! ii 8 knows it to exist. However difficult it may be, in some instances, to distinguish aright between species and varieties, as rigidly defined, there is an instinct within us which often recognizes the latter, even at first sight, m cated eye, although of course occasionally deceived, will found ; In the vegetable world this proneness to variation is self-evident ; and botanists innumerable, who have in- vestigated the causes on which the modifications of cer- tam plants have been presumed to depend, have not been behindhand in acknowledging it. Soil, climate, altitude, and a combination of other circumstances and conditions, have been successively taken into account. amount The less, as the case may be) has been conceded. " more powerful agents,^^ writes Professor Henfrey, '' en- force their general laws, but every little local action asserts its qualifying voice ■ and we see that all these irregularities and uncertainties (as we in our ignorance call them, and complain of) are necessary and important parts of a great whole,— are but isolated features of a comprehensive plan, in accordance with which aU work in concert to bring about that change absolutely indis- pensable to the existence of animal and vegetable life upon the earths surface, and that variety of conditions by which is ensured a fitting abode for each kind of its multifarious and diversified inhabitants.'' Whilst exploring 4 I i* •w 3 I 9 heights^ tlie botanist would as assuredly look for a change in the outward configuration of certain species^ which colonize equally the rich meadows and teeming ravines^ as a geographical difference is a priori antici- pated between the hard^ sturdy moimtaineer and the more enervated denizen of the plain. A daisy^ gathered on the cultivated lawn^ has usually attained a greater degree of perfection and luxuriance than its companion from the sterile heath; and the bramble which chokes up the ditches of the sheltered hedgerow^ wears a very different aspect from its stunted brother of the hills. Nor is this dependency on external circumstances less apparent in the animal kingdom also^ — the domesticated races of which every agriculturist is aware are capable of modification^ artificially^ to an almost unlimited ex- nature natural they have been proved to do when subjected to the laws and routine of agrarian science. Take the sheep^ for example^ of Dartmoor or Wales^ and compare them with those from the wolds of Lincolnshire and the downs of ■ \ Kent; or contrast the Hereford oxen with those of the midland counties^ or of the Caledonian breed^ still extant in Cadzow Forest^ and it will require but little argument to convince us how important is the operation of local circumstances in regulating the outward contour of these higher creatures. If therefore this general obedience to influences from without be self-evident in the vegetable world^, and equally traceable amongst the Manimalia, b5 \ if If I w i 't J li III I m 4|iii \- 4' 4t t 10 wL.y^ we may ask^ are tlie lower members of tlie animal creation to be denied analogous effects from the same causes t 9 We are often told that tbe Annulosa present so many anomalies in tbeir organization^ that we cannot apply the argument of analogy^ when reasoning on tbeir struc- ture and attributes ; and that we must consequently be content to leave it an open question^ as to whether or not they possess anything in common with the Verte- brata, or can be presumed to be acted upon, by external agencies, in at all a similar manner. Now, whilst there is clearly some truth in this assertion (especially as must ever remain obscurity) its fullness would be in the highest degree unpliiloso- phical; whilst, to endorse it to the extent which even its partial advocates do insist upon, would at once involve us in a host of difficulties (affecting other de- partments of natural science), the very existence of which they have themselves tacitly repudiated. cc most intellierent wr of modern times. w full of general originator, and linking all sentient things into w one great family of related fellow-Creatures :'^— and there is an amount of sagacity in the remark which it would be wise for us to digest. Throughout the whole of animated nature, it is impossible not to perceive that certain circumstances do, in the main, produce certain results. may 11 results themselves may frequently be modified (or, ap- parently, even reversed), from counter influences of divers kinds. This touches not, however, the existence of the law; and the effect is not the less specifically dependent on its own peculiar cause, becaui counter influences'^ prevail, — and because those cc efifects may chance, therefore, to be occasionally brought about by causes which may possibly seem to be identical. We should, rather, bear in mind that the agents which operate in moulding the outward contour of organic beings are various, and capable inter se of permutations r ^^^ innumerable; so that it is only on a broad scale that parallel results can be looked for in creatures severally exposed to the action of elements, which are liable to be differently compounded from what may primd facie appear to be the case : and that, consequently, where opposite ph^enomena are displayed under circumstances seemingly coincident, our first object should be [not to regard the phsenomena as indicative, that no constant result can be anticipated from causes which are simila > but), to inquire whether the circumstances in question are really coincident or not. some may unex pectedly at work, which shall enable us, so soon as it is detected, to account for the discrepancy. It is by this process alone that we can hope to make real use of analogy, without abusing it : for whilst there is danger, on the one hand, of needlessly rejecting the argument which it suggests to us, through opposite r: 'lb ■Ml ti>f p m 1 w I i m Ml mil / IIJIj t ■ltd' m U III) \. ! 12 observed organic world) from conditions which we assume to be co-ordinate, but which in fact are not so ; we may, on the other; run a similar risk (and thus fail to discern a matm^ation results). animals mere a priori belief that the lower a manner at all equivalent to that which, is self-evident in the higher ones. << To make a perfect observer in any department of science," writes Sir John Herschel, ^^an extensive ac- quaintance is requisite, not only with the particular science to which his observations relate, but with every branch of knowledge which may enable him to appre- causes. effect of le will \ any of those minute indications which often connect from He will have his eyes as it were opened, that they may occurrence to received theories, ought not to happen ; for these are the facts which serve as clews to new discoveries^/^ Inere can be no doubt that amongst a large proportion of our naturalists, differences^ as such, are too exclusively studied, iissential as their investigation is (for we could not progress a step without some presumptive notion as to the specific identity, or not, of the objects about which * Preliminary Discourse on the Study of Natural Philosophy (London, 1830), p. 132. I 1 13 we have to treat) ^ we should not forget that there are other questions^ likewise^ which ought to occupy our attention in^ at any rate^ an almost equal degree^ — as being of eminent significance in guiding us to a correct nterpretation of the phsenomena with which we have to deal. Such are^ more especially^ similitudes and ana- logies^ in their widest sense^ — which are too often neglected^ even by those who admit the necessity of recognizing them where they may be shown to exist. Lord Bacon^ in referring to a similar tendency amongst a certain section of the naturalists of his day^ remarks (though perhaps his love of analogies may have led him to somewhat overrate their importance) : ^''Up to this time the industry of men has been great^ and very curi- ous in marking the variety of things^ and explaining the accurate differences of animals^ herbs^ and fossils^ — the chief part of which are the mere sport of Nature_, rather than serious and of use toward the sciences. Such things tend to our enjoyment^ and sometimes to even practical use; but little or nothing towards an insight into Nature. And so our labour is to be turned to in- quiry into^ and notice of, similitudes and analogies^ both in the whole and in the parts of things : for these are they which unite Nature^ and begin to establish / ■J sciences <^ ^' * "Magna enim hucusque atque adeo curiosa fait hominum in- dustrial iu notanda rerum varietate^ atque explicandis accuratis animalium, berbarum. et fossilium differentiis ; quarum plera^que ttiagis sunt lusus naturae, quam serine aUcujus utilitatis versus tikfi I *'\ Uk I 14 I believe that^ if analogies were more carefully studied in the lower departments of tlie animal kingdom^ we should be less inclined to deny some sort of uniformity to the action of elements and conditions which^ by a law of Nature^ must at times operate equally upon the various and dissimilar members of the organic creation. Amongst the Insecta^ where the individuals exist in such multitudes that accuracy in generalizations concerning them^ becomes^ as it were^ peculiarly within our reach^ this doctrine cannot be too rigidly insisted upon ; and it is not difficult to foresee that^ should the principle of external disturbing influences ever be admitted by ento- mologists to the extent which it has been acnentprl bv our ^^ species ^^ will have to submit to a process of elimination and inquiry^ which at present would be well nigh incre- dible. time indeed^ considering the innovations of nomenclature which it would necessitate^ it will never arrive at all; r yet the fact remains the same^ that^ if analogy with more disallowed us^ during our researches into the insect tribes^ or if similar causes may be presumed to have somewhat similar effects in opposite sections of the scientias. Faciunt certe hujusmodi res ad delectationem, atque etiam quandoque ad praxin; verum ad introspiciendam naturam parum aut nihil. Itaque convertenda plane est opera ad inquiren- das et notandas remm similitudines et analoga, tarn in integralibus, quam partibus : illse enim sunt, quae naturam uniunt, et constituere scientias incipiunt." — Novum Organum, lib. ii. 27. \ '[ '( i [^ /" 15 animate worlds an enlargement of onr prescribed limits^ for specific variation^ ought in reality to follow (sooner or later) as an inevitable consequence. In whicbever ligbt^ therefore^ insect aberration is Viewed by us^ — whetber as a matter of experience (which^ being self-evident^ will satisfy the practical observer)^ or as probable from analogy (which will hardly be denied_j at any rate to a certain extent^ by even the most theo- retical) ^ — we affirm that if doeSy ipso facto ^ ewist. cc There is no similitude in Nature that owneth not also to a difference '/^ let this be constantly borne in mind, for it is a truism almost beyond controversy, and one which, to a reflective mind, will scarcely admit of a doubt . r It will be perceived, from the above remarks, that I draw a distinction between insects which simply vary (that is to say, which aberr from their normal state), and those which afford (in. the sense as enunciated in the last chapter) one or more actual ^Warieties,^^ — technically so called : and it will be further gathered, that, whilst I regard the former as universally to be met with, the latter are, on the contrary, of only occasional occurrence. That positive and well-defined varieties, or races, should be confined to certain species, is not re- markable ; but that every individual insect should difier, however slightly, from its nearest relation and ally, may perhaps require some few words of explanation, even to a naturalist. It is not essential however to our present subject (which is merely a plea for specific variation fr mm I r \ 1 I \ 'I I lilt 16 generally^ as commonly understood) tliat any sucli dogma should be propounded; nevertheless^ since all analogy teaches us to anticipate it^ and observation tends more and more^ as our knowledge advances^ to corrobo- rate the fact^ I shall be pardoned for venturing a passing thought upon a question even thus difficult of demon- stration. Perhaps we are too prone to regard those specific characters^, which are so subtle that they cannot be grasped by our clumsy faculties except in their broadest and plainest features^ as incapable of fluctuation. Yet a practised eye can detect discrepancies innumerable in specimens which appear absolutely alike to one that is uneducated ; whilst a third person^ better qualified stilly will trace out other and more delicate distinctions^ with even greater precision. And thus it is that we rise^ step by step^ even amongst the humbler representatives of the animal kingdom^ to the comprehension of that great truth which is so conspicuous in the nobler ones^ and which we have already summoned to our aid^ that ^^ there is no similitude in Nature which owneth not also to a difference.^^ Let us not forget that the sphere of our senses is limited; and that^ although tuition will do much to enlarge their capacity for perception^ we are at the best but a dim- sighted race : hence^ we should be careful to avoid conclusions which are not warranted by our gradually brighter, no less assuredly True may I 1 m 17 to appreciate the differences between indiyidnals without a rigid inspection^ and that sometimes we may fail to do so even when the objects are critically examined; yet the fact that new pecnliarities do nn questionably open out upon us^ as we become more and more trained for the recognition of them^ ought to warn us that others may exist likewise, despite our primd-facie conclusions ; whilst analogy with what we know to be the case in other departments of the organic world should suggest, unless indeed there is presumptive evidence to the con- trary, that they in all probability do. The Alpine range, when seen from afar, appears a monotonous mass of a dull uniform hue ; and nothing, r of all the wondrous details which it includes, can be distinguished, except perchance the outline of its jagged peaks projected in faint rehef against the distant sky. One by one, however, as we approach it, inequalities present themselves ; the surface which lately seemed so uniform and grey that it could be compared only to a cloud, is found to be cleft by ravines ; and valleys, in all their magnificence and breadth, expand slowly to our view. Yet, marvellous as is the change, this is not all : wood and water, without which the landscape would be barren, are in turn revealed ; whilst the play of light and shade upon the mountain-slopes proclaims at length that the picture is well nigh complete. Still more to be disclosed does in reality remain ; and we must advance nearer yet if we would either fully realise the whole, or enter into the surprising minutise of each of its com- fl m ii J . 'tifflj I H ' X H - ^ - _ ^T" P 1 18 ponent parts wi have been just discussing. Wlien contemplated in mass^ and by an uneducated eye^ tliem may becomes more gradually made ■until at last we can detect modifications innumerable, throughout the entire length of the living panorama ; and are enabled to endorse the belief (repugnant a priori though it be), that individual variations suggest, are not incompatible with specific similitudes. ^i 19 CHAPTER III. CAUSES OP VARIATION. " It is not impossible/^ says a writer of tlie last century, " that such laws of Nature, and such a series of causes and effects, may have been originally designed, that not only general provisions may liave been made for the several species of beings^ but that even particular cases (at least many of them) may have been provided for without innovations in the course of Nature"^'/^ And let mer tion, unsupported by evidence (if not actually circum- stantial, at least) strongly presumptive ; since the further we penetrate into the ramifications of the organic world, the less are we inclined to ignore the operation of those modifvmg mnuences which our tells us do everywhere exist. endeavour to trace out by slow, inductive processes those second- ary agents, by the assistance of which a large propor- omena much is no insignificant task; yet how from without have the students in such fields of research frequently to endure ! A fact many times repeated, and which conies within our daily experience, is too often * Religion of Nature Delineated, p. 103. i\ -m - 1 L\ 1 1 i i i ,( m •)■*■ ! • I 20 looked matter man who regards truth as valuable^ for its own come appreciation of results, whether they be of rare or con- stant occurrence, will have learnt to pronounce nothing sm chain of knowledge which would be broken and im- perfect without it. A spirit inquiry^ however, is more fidently anticipate the period when such reproaches will have for ever died away. Natural history, in all its branches, will then advance more rapidly than hereto- fore, and each separate labourer, in his own peculiar province, will breathe a more genial atmosphere ; whilst observation and reason, mutually dependent on each other, will work in concert more effectually. ^' Reason hout observation,^^ writes the author above quoted, wi ^\* i Wv i i Kill, t i U' I ■•im\ » ,'i till I I ■ I I ( i ■:.!*< » 1 38 \ .- ■^ k; V \\ islands present parallel modifications^ where that line is to be drawn. Meanwhile^ how far geographical va- rieties of this kindj concerning the non-specific claims of which confessedly but little donbt can exists may lead to the explanation of the Transatlantic ones just referred to^ I will not venture to suggest. Yet certain it is^ that the one case bears directly on the other ; and that^ if we can prove that common European insects^ when iso- lated in the ocean^ become in nearly all cases more or less modified externally in form^ there is at least pre- sumptive evidence that the law will hold good on a wider scale^ and may be extended^ not only to the Atlantic itself^ but even to countries beyond. The dif- ferences of the present Dromius from its more northern representatives are^ as just stated^ small; nevertheless^ since they are fia^ed^ those naturalists Avho do not believe in geographical influence might choose to consider them of sufiicient importance to erect a new species upon. But after a careful comparison of this with other insects similarly circumstanced^ I am convinced that the modi- elv local ones, and such •i 4 ( me may agencies of latitude and isolation^ and the consequently altered habits of the creature^ which is thus compelled to seek alpine localities in lieu of its natural ones"^/^ /^ menus marginatus^ Linn._, and the Anthicus fenestratus, Schmidt^ which occur almost exclusively in the lower * Insecta Maderensia (London^ 1854), pp. 7? 8, 9. ■ \ I I 39 Madeira moiuitain toDS : eacli, moreover whicli are just sufficient (although slight) to distinguish them from their European representatives. And if we inquire^ on the other hand^ into the abo- riginal species of those islands, — or, at any rate, into such of them whose naturally acquired range embraces the opposite extremes of atmosphere, — we shall detect no less surely (albeit within a narrc climatal action on insect form. WolL. ' Helops confi , " varies according to the altitude at which it is found ; being usually deeply striated and rugose on its much on its upper limits. specimens indeed niountain diminished H. The Pecte Maderensis, WolL, which ranges from "Knirp +.hp, sea. to the summits of the 1 although usually with pale legs, is distinguished by having its femora almost invariably dusky when on its highest elevation; and, following out the analogy I WolL. should with that beetle, the Trechus alticola, perhaps be regarded as an alpine state of the T. custos. assumes land heights a very different aspect to what it does in the regions below, being generally more piceous and convex, altogether broader (in proportion) and shorter, and * Insecta Maderensia, p. 516. ! 1 X V I 1 1 ■'.T- > li I : ' mi ii ( (ii|i; if a i»4 i i _ _ Hr ll! i^k 40 with both sexes (though, of course^ especially the male) shining. Nor is this nrincinle of tonop-ranhinal variahilitv (ilia result Notiophili u are extremely unstable_, ;ure modifications, thouerh more would e N. s own found summits of the mountains ; but at that elevation it be- comes liable to great alternations of colour^ ranging from pale brassy-brown^ with the apex testaceous, into deep black. The sculpture, however, perhaps is nearly as much dependent on other circumstances for its mo- dification as upon altitude^ since it seems tolerably clear that proximity to the sea-shore, especially where the localities are saline, will frequently produce a more faintly impressed surface^.^^ It has indeed been lately suggested, that the Helobia nivalis, Payk., may be per- haps, after all, but a mountain variety of the H. brevi^ collis ; the Leistus montanus, Steph., of the L.falvibarbis, and the Patrobus septentrionis, Dej., of the P. ewcavatus ; but of this I think further proof is needed^ seeing that certain species do appear to exist which are strictly alpine (that is to say, which have not been, severally, detected in the lower regions of more northern zones) ; and^ in most instances, where aberrations are to be met * Insecta Maderensia, p. 17. I k I ^ . / '1 41 from from posed to liave originally sprung obtain elevated portions of tLe same country), i intermediate links ? Now I am not aware less- links have, in tlie examples above cited, ever been ob- \ many districts where tlie quasi variety is found, the descend- enitor do occur in beneath. remarked become inconstant '. ; maximum _ it above the sea; and I have but Httle doubt that the C. fasciatopundata*, Germ., from Asia Minor and Turkey, is the C. sylvatica modified by a long residence in elevated regions. And so it is with the ChrysomeliB, many of which become, in the loftiest altitudes to which they ascend (as I have noticed at the head of the St. Gothard Pass of the Swiss Alps), subject to unusual changes, both in lustre and hue . The above examples, although few and indiscriminately selected, will serve to illustrate the principle which we have been contending for,— that climatal influences generally, may (and in most instances do) tend to affect, more or less directly, the outward contour of the insect I I tribes. will be remarked * I possess specimens of this insect captured on the summit of Mount Olympus by my friend E. Armitage, Esq., who is also of opinion that it may be but a mountain state of the C. sylvatica, Linn. .; I I 1 VA- Q{-\' i u ^ A '!■ i "I Mn i I m I ^- \\ 14 iiiM ■'W% til \ V " ^ -i i n 42 cited no great disturbing power has been made evident^ tbe aberrations to whicli we bave appealed being, most of tbem, comparatively minute. This, however, is simply in harmony with the belief which we have already expressed, that climatal causes, when taken singly and alone, are not of primary importance whilst discussing the question of specific modification. It remains for us, in the following sections, to inquire, whether there are any other elements at work from which greater results are to be expected. Meanwhile, let us not forget that differences mai/ be, in the strictest sense, significant, even whilst small ; and that it is their constancy ^ rather than their magnitude, which more particularly concerns us in the present treatise, seeing that it is with reference to those distinctions which are less conspicuous that the greatest amount of misunderstanding (through the fact of their being fixed) usually prevails ; whilst it is our main object to show that dissimilarities do not neces^ sarily imply the specific isolation of the creatures which display them, merely because they are, in their several localities, permanent. t -■ i\ § II. Temporary heat or cold^ of an unusual degree. It is perhaps unnecessary that the action of temporary heat and cold, of an unusual degree, should be considered under a separate head from that of climatal causes gene- rally; nevertheless, since the latter are, in a certain sense, permanent in their operation, it may be thought F \ I i ..-' - ^ I I i 43 + desirable tliat I shouia offer a few words on tlie effect of sudden exceptions to the ordinary routine of things, such as, for instance, seasons of peculiar intensity. It does not however appear that any very important modi- fications do often occur from conditions thus abnormal, and as it were accidentally brought about : on the con- trary, indeed, it is a well-known fact, that the members of the insect world are singularly independent of such + same manner times of maturation part external development is for the most their control. Yet, in spite of this, results are wont to happen, ever and anon, from ^^,,v^c.+«^/^ria oa +l»mia-Ti if. were a fundamental from axiom, that every agent which Nature ;gula: it may voice. I believe from typical state, in insect form, which has been observed to om ance of undue heat or cold, is curiously enough an or- ganic one. enlar; wm must proportion of the Coleoptera (especially the Carabid(2) metathoracic organs of flight. Many my more narticularlv drawn Ml. •K^h •9 iJi'. i t ■1 . ■ r . T 1 4 ! sm\ \ i* IN . >" ^ - ^ 44 have the hind wings at one time ample^ at another rudi- mentary^ and at a third nearly obsolete. Now^ although other causes^ hereafter to he noticed^ would seem to have far greater power than climatal ones in permanently regulating the size and capacity of these appendages ; I think it will be found on examination (and I may add that Mr. Westwood is of the same opinion ^)^ that the greater or less development of them may be frequently explained by the unusual severity of the seasons. My own researches would certainly tend to prove^ that heat does (in the main) favour^ and cold retard^ their pre- sence. Exceptions (often rendered intelligible from the evident working of counter influences) will of course arise in abundance to this hypothesis ; yet my impression is thatj upon a broad scale^ it will stand the ordeal of a rigid inquiry. Speaking of certain representatives of the Hymen- optera {Chalcidida) , Mr. Westwood observes: ^' curious peculiarity exists in one at least of tliese apterous species^ which, has been noticed by no previous A author, namely, Choreius ineptus, Westw which. although ordinarily found in an apterous state, was discovered by me in considerable numbers during the hot summer of 1835, with wings f''. And, touchmg the irregularity of the alary organs in the Homopterous Fulgorid(B, he remarks : " Other instances, in which the wings undergo a deficiency of development, occur in the * Introduction to the Modern Classification of Insects (London, 1840), ii. p. 473. t Id. ii. p. 158. I V /" 45 genus Belphax, tlie majority of which, in our English more one half of the ahdomen the terminal membrane being deficient, as well as the hind wings. In certain seasons, however, especially hot ones, the wings are folly Mr. Curtis has indeed formed specimens into a different genus, Crio- morphus. more stimulating Aitnougn tne resuii oi a ii\}jy:^ ^Liinuxcxtixig 0^1.3- ^^^j be often neutralized by that of isolation (which, as we amon of species, in weakening, and frequently rendering abor- from counter J on tlie alary system of insects, no less than when tem- porarily applied. The consideration of this, however, belongs strictly to the preceding pages, and we will not therefore discuss it here. The common Bed-bug {Cimex ledularius, Linn.) is almost invariably apterous, or with very short rudimental hemelytra; yet Scopoli {Ent. Cam. p. 354) mentions its occurrence with perfect Fallen, also, and Latreille, state that it has wings "Westwood remarks \. has been reported as occasionally winged in the East seem these examples, as in numerous others which are on may * Introduction to the Modern Classification of Insects, ii. ^ ■ p .431. X s:nJ »^ ! tt mMik n^ mi ^^ i 'isii N^ y if i !fl' I 3 I 46 as temporarily applied (in an unusual degree)^ or througli the accidental transportation of the insect into a naturally warmer atmosphere. § III. Nature of the country and of the soil. Before we proceed to inquire to what extent the out- ward aspect of insects is liable to be controlled by the physical state of the areas in which they severally obtain^ it may not be altogether out of place to offer a few reflections on the superiority which some regions possess intrinsically over others^ both for the increase and diffusion of the animal tribes. To suppose that all countries within the same parallels of latitude are equally favourable for the development of life (not to mention the after-dispersion of it)^is contrary to experi- ence ; for although (as we have already pointed out) the organic world does certainly^ when viewed in the mass^ approach its maximum as we near the tropics^ there are at the same time so many violations of this law^ that we cannot admit its operation except in a broad and general i sense. In a former section of this chapter^ I drew attention to the fact_, that certain islands^ equatorial and subaustral^ are anything but suggestive of their actual positions with respect to the line of central heat on the surface of the earth. It was with regard to climate alone^ however r that I wished them to be understood: and it is not until now that I have ventured to urge the necessity of \ .. . # /" I 47 would desire to recognize anything like design and adaptation (I will hardly call it cause and effect) hetween the con- thin It is almost needless to add, that there are many elements to he considered, such as local atmospheric conditions, excess or deficiency of electricity, superabundant moisture, diminished light, and the geological composition of the soil, before we can hope either to appreciate zoological phsenomena as a whole, or to reconcile the apparent inconsistencies which they are accustomed to display. Mr. Darwin, to whom we are indebted for so much valuable information concerning the natural history of various portions of the world, in his notes on Tierra del Fuego, observes : " Beetles occur in very small num- bers ; it was long before T could believe that a country as large as S cotland, covered with vegetable productions could Heteromera s of HarpalidcB The vegetable- emme tropics, are here almost entirely absent. I saw very few flies, butterflies, or bees, and no crickets or Orthoptera. found I have climate general appearance of Tierra del Fuego with that of Patagonia ; and the difference is strongly exemplified m the entomology. I do not believe they have one species in common; certainly the general character of the wm U I i «)*>! ii| : ■ til 1^1 I mt 48 insects is widely dissimilar "^/^ Now with primary considerations : first^ that there must exist some great peculiarity (apart from climate) in a region the fauna of which is thus singularly constituted; and, secondly_, that latitude (however important it may he in a comprehensive point of view) must exercise in this case a very secondary influence, to allow of localities separated only hy the Straits of Magellan to present differences thus extraordinary. Although so dissimilar in many respects, Madeira and Tierra del Fuego have evidently much in common as regards the conditions which they afford for the increase of organic life. Mr. Darwin describes the latter ^ a mountainous region, partly submerged in the ^ So is Madeira. He also adds, that it is ^^ covered to the water's edge with one dense, gloomy forest/' that ^^ to find an acre of level land in any part of the country is most rare ;'' and that ^^ within the forest, the as sea. ground is concealed by a mass putrefyi matter yields to the foot.'' state t; and such it Madeira * Journal of Researches, p. 238. t That I may not be misunderstood by those of my readers who conceive Madeira to be a kind of ^^ arva beata/^ with the skv for ever blue, and (as a consequence) an unclouded sun; I would re- peat, that I am not speaking of the vicinity of Funchal only (from which the invahds, who resort thither for their health, almost exclusively draw their deductions), but of Madeira^ — and, more- I ^-^ v-1 ■-+" v^---* 49 i ■*ii H I \ J -7 \ .'- 8ti |[ f 4* 56 Having then disposed of this preliminary appendage to our inquiry^ by expressing onr belief (which I am satisfied that observation will tend more and more to corroborate) that certain countries and spots are by constitution more favourable than others for the increase (apart from the after dissemination) of the insect tribes^ — and that too through local influences amongst which mere heat and cold are but secondary in importance j let us proceed to consider^ r how far the nature of the several districts may assist us in accounting for some of those numerous aberrations from the typical state which various insects are accus- tomed to display^ and on which it has too often hap- pened that ^^ ^^ (so called) have been attempted to be established. I may premise however^ that^ whilst (as already urged) I would regard climate per se as sub- sidiary to many other agents^ I would not wish to ignore its action altogether even under the present sec- tion_, since in combination with peculiar circumstances and conditions it may have (and probably has) consider- ■—.J * — ^ '- able controlling power : nevertheless I would desire it to inferior wi under of greater significance than itself. If therefore preceding heads it has been treated (so far at least as the exceptions would permit) as a great geographical principle^ possessing a certain modifying quality on a large scale^ let us now merely recognize it to the extent in which we are actually compelled to do^ when dealing with areas of smaller magnitude^ — namely as a ^o/^ographical one. \ ^ i^ki* \ 57 From amongst tlie many results wliicli I liave been im I leave it for others to decide) with certain special situa- tions^ I would gular stancy whicli numerous insects are liable to when ex- isting on the coast^ — and wbicb frequently c them from inland types^ that^ without local knowledge to guide mi distinct . comments this fact in the pages of the 'Zoologist'; which, as I modify transcribe at length : .•^ ~\ " The extraordinary changes which many insects are ^ subject to when occurring near the sea, is a fact worthy of notice, and one which I do not remember to have seen recorded. The strictly maritime species must be left out of the question -, for although many of them are exceedingly variable both in size and colour, still we have no means of ascertaining whether that variation is referable to the locality in which they are placed, — for, never being found inland, nobody can have an opportu- nity of asserting that the same changes would not take place, were they to occur in positions far removed from the influence of the sea. When we find, however, the same insects in profusion both inland and on the coast, and observe also numerous and marked deviations from the typical forms peculiar to the latter situation ; then, a priori, we have strong presumptive evidence that the D 5 y ■ 4 ft « 1 li.-t -fl I I I Ira ill !i:t M ii i; f. t. I I 'i '<( 1* M 1 I : ) I ^ J }' M II 58 Stif ^ »■ ^ ii. *-# { M changes in question are the result of local circumstances^ and not referable to chance. The alteration in size I have almost always observed to be from large to small^ and scarcely ever the reverse ; whereas in colour the change takes place very nearly as much from hght to dark as it does from dark to light : nevertheless the majority of instances I possess come under the latter department. It has been remarked that all the speci- mens of Mesites Tardily which I captured in Devonshire^ were much smaller than the original series taken by Mr. Tardy at Powerscourt Waterfall^ in the county of Wicldow j and so decided was the difference^ that many of my friends^ at first sight^ concluded the two to be distinct species. This^ however, I consider entirely owing to their locality, for my specimens were found only on the coast, and Mr. Tardy^s at a coi distance inland. And, inasmuch of these instances rested on mere individual examples, but on long and conspicuous series, the certainty of the change from large to small was the more apparent. Mr. Holme of Oxford mentions having taken Olisthopus rotundatus in the Scilly Islands, in great profusion, none of the specimens of which exceeded two lines and a half in length. At Whitsand Bay in Cornwall I have captured Gymnaetron Campanul(Ey none of which exceeded three- quarters of a line, — the usual length being from a line to a line and three-quarters. Anthonomus ater^ the average length of which is two lines, I have taken a series of in Lundy Island, none of which exceeded one. ^ 11 V- H -. I - _y -"-■^ -V ^ 59 In the same locality^ also^ tlie common Ceutorhynchus contractus scarcely ever readies its natnral size ; and is, moreover^ so variable in colour, that I was long before I could persuade myself that the species was not distinct. Instead of the bluish-black elytra which I had always considered invariable, they all possess a yellowish or brassy tinge ; and the legs, instead of being black, are in most instances entirely of a light yellow,; — and in all, more or less inclined to that colour. I have received from Mr. Hardy, of Gateshead, specimens of Haltica rufipes^y captured by him on the coast, in which the entire insect is of a uniform brownish-red hue. Of the rare Mantura Chrysanthemi I have taken beautiful Mount Edfifcumbe many of the brassy-brown of the ordinary specimens : also, in specimens pJiorus testaceus. manner emarkable * I perceive, on reference to the original examples^ still in my collection, that this was wrongly quoted as the Haltica rufipes. It is the H. exoleta, Fabr., and it is thus entered in Messrs. Hardy and Bold's ' Catalome of the Insects of Northumberland and Durham ;' where they make the observation, "variable in colour; specimens from the sea-coast are frequently of a dark mahogany tint/' I have myself indeed, since I communicated the above remarks to the ' Zoologist/ taken its precise counterpart, in abundance, along the Yorkshire coast,— from Bridhngton to the extremity of Flamburough Head; so that it may perhaps be regarded as a topographical state which is more especially pecuhar to the eastern shores of England, north of the Humber. i / I 1 . i H :: fi \ \ i r 4 I ^ \ I \ 1. h ■ f| J I 'i \ % I r4» Hit lit t^: ^t IV ii'- I" #ii tit I fc,, t 11 }-^ ^ 'J- I 60 mentioned are sufficient to verify my tions^ of the extegm^Jiabili imme diate inflnence of tlie sea. How to account for it^ I know not. I mention it as a mere fact^ and leave it for others to assign a reason for its existence"^.^^ Apparently dependent^ in a large measure^ on the same circumstance (namely proximity to the coast) ^ the Bembidium saxatilej Gyll.^ so common at the edges of the mountain streams in the north of England^ in Scot- land^ and throughout a portion of Ireland^ presents itself along our southern shores in the form of a permanent variety ; being, as the Rev. J. F. Dawson remarks^ ^^more depressed^ never narrower in front (the sides therefore more parallel), whilst the colour is always much paler and the spots larger, — that before the apex being round and very conspicu-ous, and the anterior one occasionally expanding over the surface very considerably f.^^ I have taken it in profusion on the coasts of the Isle of Wight, Dorsetshire, and Devon. And so with the Cistela suU phurea^ Linn., which in certain maritime localities (as I have particularly noticed on the sand-hills at Deal) is liable to become so dark in colouring, that, without the intermediate shades to judge from (which however may mi mi A Psylliodes in Lundy Island, allied to (if not identical % ■ * Zoologist, iv. pp. 1283, 1284. t Geodepliaga Britannica (London, 1854), p. 186. i i^ \ 4 -*_ \ li ■ J I 1 ! iH \ 61 Wl in from limits of li2:lit yellow and dark metallic ;; the normal mi from the latter, did not observation on the spot decide without Another curious example of the effect of local m amon in on the external aspect of insects exists in the ApJiodius plagiatus, Lmn., ■which in this country is generally deep black. It is noticing/^ I remarked in the a circumstance worth ' Zoologist; in 1846, " that the form which is looked upon by the continental naturalists as the variety, is in England evidently the typical one,— for out of about sixty specimens which I captured [at Tenby in South j Wales], only two possess the conspicuous red dashes on the elytra which are considered abroad as the almost invariable accompaniment." I have observed the same peculiarity in the flat and damp spots between the sand- hills at Deal, where I have never detected a single in- dividual which is not perfectly dark ; and I believe that ■ the greater number of the specimens which were ori- ^ same geographical characteristics; whilst those which ^^^ were found near the more inland towns of Peterborough * Zoologist, iii. p. 900. \ n i; I ( H [■ I ■; 1^4. U ■ i> ■■ 62 i Ht *' *^ )« *> w !*«■ i.: \ \t: ^r 4^ \ ^ WE . flf--t>i ir W 4^:' I # (>! L» ^' I and Norwicli present a larger proportion of the ordinary European state. The blood-red dashes, however^ with which the elytra of numerous insects are adorned_, I have constantly remarked possess a singular tendency to be- come evanescent. It is indeed almost diagnostic of the /genus Gymnaetron, either that its representatives should he thus ornamented typically, or else that those which are normally black should^ when they vary, keep in view^ as it were^ this principle for their wanderers to subscribe to. Thns^ I have no doubt that the G. VeroniccE, Germ, is but a variety of the G. niger, — an opinion which T expressed in the ''Zoologist^ nine years ago. Whilst commenting on the Coleoptera of Dorsetshire^ I then my own part I must om the G, niger, for red dashes on the elytra seem naturally should therefore have suspected that^ had occasional aberrations from a black type existed (which is not unlikely), those would probablv assume common ^ ^y The Bembidium bistriatwn, Dufts.^ is usually much paler when found in saline districts (under which circum- stances it was described as a distinct M Stephens) than when occurring in more inland positions. The Blemus areolatus, Creutz., I have frequently re- marked is similarly affected in brackish places : and I think it far from improbable that the Stenolophus Skrim- * Zoologist, V. p. 1941. ^ i ■* 63 modification marine S. TeutonuSy Schr. fasciatus may in point, — the specimens wliicli are collected near the coast being for the most part singularly pale. In M I'erte observes : '' II y a seulement lien de remarquer que eneralement pales que ceux des contrees orientales de TEurope, et que V lourvus entierement in much manner ■m ment repandu de Teau salee. ncontre non-seulement sur meme de la Baltique, mais ^ tels nue celui de Manns- feld, en Saxe. Ceua? de cette derniere localite sont gene- r\ ceux me est dans le meme cas que quelques autres Anthicus, dont les varietes les plus foncees appartiennent au nord de midit Whilst numerous on proximity to the sea, we may just notice the marked ten- * Monographic des Anthicus (Paris, 1848), p. 149. t Id: pp. 127, 128. I I h % I J 1 t - -1 I |l il I tf ■I i i * \ I 4 t 1 1^ ( (^i ■fi? ** ■ -V JU^ It IT 14^ l«»r »4lf m- fl>rK «■'■ ^i: II If t m 4 m\%' t> V 4 S i i \ < d ^ \ ,v /^ t £ ^ t* V ^-. o ■^ ■ ^ ^ ■ 64 -* mV dency winch even tlie in^eQt^ peculiar to saline spots would seem in a large measure to possess^, of converging^ more or less obviously^ to a lurid-testaceous^ or pale brassy bue^ in tbeii; colouring. True it is tbat we cannot (as above suggested) deduce any evidence of direct physical modi- fications from amongst species which are strictly mari- time^ — seeing that we have no means of judging in such instances whether similar phsenomena would or would not be produced in central districts also : nevertheless we may perhaps detect in this general law some slight indication of the effects which an atmosphere and soil constantly impregnated with salt would be likely to bring about in the external aspect of those members of the insect tribes whose range is sufficiently extensive to expose them to its operation. The bare mention of such names as Nebria complanata and livida^ Calathus mollis^ Pogonus luridipennis ^ Trechus lapidosus^ Aepus marinus and Robinii^ Cillenum laterale^ Bembidium scu~ tellarey ephippium and pallidipenne^ Ochthebius marinus ^ Psylliodes marcida^ Phaleria cadaverina^ Helops testa- ceuSy and Anthicus instabilisy so eminently characteristic as they are of briny situations^ wiU at once appeal to our native entomologists ; whilst the acknowledgement F of the same principle is no less conspicuous in a host of other species which are not included in the British fauna. Hence^ when we see the tendencies of coloration (not to mention other particulars^ often readily apparent) essentially the same^ both in insects which are peculiar - r X V— ■ — V 4 L ■ I r 65 om certain regions or localities, it is impossible not to asso- ciate some inherent controlling power witli the regions themselves ; and we are driven to the conclusion, that either well-defined races have been gradually shaped out, by means of the physical influences to which they have been exposed, or else that the species themselves (as witnessed by the intermediate geographical links, which, although sometimes rare, are in all instances to be found) do assuredly merge into each other. In addition to those which we have been just discuss- ing, there are other influences (equally independent of mere heat and cold) by which insect modifications may be brought about, — modifications moreover must itry and of the soil m 3ry few examples, howe r must suffice for our t purpose Madeira prothoracic disk (and with its elytral strise less deeply impressed), than it is in Algeria and Spain. The Madeiran snecimens of the Aphodius nitiduluSy Fabr., more lated, than their northern analogues; as are also, in the latter respect, those of the Clypeaster pusillus, Gyll. Helfi m Madeiran is m believe that the Achenium Har Sicily; and I Heer, of those / r iU \ \ \ \. ) t I i i ! S^^'t i r t 1 P^ >-*- "v. ' ■i:- ^ I i ■i- u -^ It f-^- ^ t ! ■(TS 1 i m* ,t r i -.-^ r^ ti J i 1 t I i I ^ \ . f Jl^ mi' ^\ -ft- II HH m\i tt t I «i I -\ t i iv / 66 islands^ is but a local state of the A. depressiim^ Grav._, of Central Europe. The Bembidium tabellatum and Schmidtiiy WolL^ ; modifications of tL L latitudes: and the geographical Malthodes Kiesenwetteri, Woll European ilf, would Calcareous deposits cacy in regulating the outward aspect of such species as are able to adapt themselves to different geological districts ; and when in juxtaposition with the shore^ their effects are often very conspicuous. The Dromkis arenicola. WolL, is the Portosantan representative of D Made proper and throughout Europe)^ I believe it to be in reality but a local condition of it^ occasioned by a resi- dence through a long series of ages on a calcareous soil. For the same reason perhaps (though assisted,, in all probability, by the qualifying power of isolation), the Hadnis illotus^ Wolh, may b( Madeiran H, In like manner, the Bem- Woll., which in Madeira frequently so dark that its elytral patches are sub- seldom assumes more calcareous than the central mass streams th muriate of times almost ■being Some districts seem to be r r / »4 * A 4 I / 'f\ h^ t * -\ !■■' J , T / '■ 67 more enerally, tlian otliers . The \ ^ ^,*#».. neighbourliooa of Ipswich, in our own country, has Mr of Ireland. :ed a similar tend common Haliplu the Blackwater river, in the county of Cork, is usually so dark and suffused in colouring, that it might he almost taken for a distinct species,— its fasciae, especially the hinder ones, being occasionally evanescent. One more example must satisfy us under this section, —namely, the Harpalus vividus, Dej., of the Madeiran group. So curiously is that insect affected by the nature of the areas through which it successively as- cends, and that too irrespectively of heat and cold (as may be gathered from the fact that its phases on the shore and upland heights are well nigh coincident), that it may be appropriately singled out as a concluding in- stance of the effects of those obscure local influences to which we have been drawing attention. "Ranging from the beach to the extreme summits of the loftiest mountains, accommodating itself at one time to a low barren rock of 20 yards circumference, at another to the deep-wooded ravines of intermediate altitudes, around which the clouds perpetually cling, and where vegeta- tion and decay are ever rampant, or harbouring beneath the rough basaltic blocks of the weather-beaten peaks (6000 feet above the sea) ; we should naturally expect, * Proceedings of the Entomological Society of London (Part 3, New Series), p. 4. y^ fjM' ^ Rit »i' . I \ w \ i I I :<#i. *■ ■ ■ 9\i ft »^ ^^■n t 1. ^i ■i m . 4^ I rffl^ 1 I 68 some slight modifications localities 3e every- ward structure^ acco differed in condition, where the case. I only by a carefd observation on the spot that an insect like the present one can be properly understood ; for, to am moreover m it is but too many might be established on undoubted varieties^ where there exists a desire for creating them, and where our sole knowledge is gathered from a few stray specimens collected by another person, and unaccompanied by local information to render the aberrations intelligible. For it must be tracked from the shore to an elevation of more than 6000 feet before we are enabled to discern I the causes by which its development is controlled, or even to connect by slow and easy gradations its opposite extremes of form. interesting the distance between its variations does not increase in proportion to the distance between its altitudes. On the contrary, it would seem to pass through its minimum maximum from om limits of the sylvan districts, — it becomes modified, and almost in a similar manner, person who had visited Madeira and had gradually Thus, to a up specimens on the coast, and to another who had per- chance penetrated into the interior, as passing visitors t I 1 t tti i il /' 69 > , I r from the vessels are accustomed to do^ and had brought away examples from the wooded mountain-slopes^ the two insects would appear altogether distinct. For^ com- mencing on the level of the beach^ the usual type is broadj flat^ more or less opake^ with the prothorax almost impunctate^ and the elytra soldered together. As we ascend higher^ the breadth invariably diminishes^ the brightness^ and depth of sculpture^ seem (up to a certain altitude) to increase^ and the elytra are seldom^ or but very imperfectly united ; until^ on entering the lower limits of the forest region^ at an elevation per- haps, ore rotundo, of 3000 feet, we find that it has gradually put on a very different aspect, — being small, narrow, bright, convex, comparatively ovate and deeply striated ; the legs and antennse have become exceedingly pale j the prothorax has altered considerably in shape, being much narrowed behind and punctured; and the elytra are nearly always free. In this state it continues for about 1500 feet; when again emerging into the broad daylight of the open hills, it recommences to mould itself as it did below ; until, having reached the summits of the loftiest peaks, more than 6000 feet above the sea, it has almost (though not entirely) assumed the features which characterized it on the shores beneath^.^'' 11 \ \ \ * Insecta Maderensia, pp. 55, 56. I I y1 > ! . 1 I /. :U'^ t a: w i n- M « 1.41 m^ 19 M . 1 )#/ |. 'Hi '^ li :|||' I' *K ♦! f r iK 70 ^ IV. Isolation ; and exposure to a stormy atmosphere. Having in the preceding pages tonclied upon the sub- ject of insect variability/ as the occasional result^ to a greater or less extent^ of climatal and other influences ; let us now proceed to consider the importance of a certain physical condition^ Avhich will be founds I believe^ more fy natural history islands^ both in theory and practice^ must be aware of many y countered^ before the several phsenomena can be satis- factorily explained. Laying aside those forms which are manifestly endemic (the numerical proportion of which usually accords with the distance from the nearest mainland) ,'^again and again are we baffled by the near r resemblance of the various creatures to continental types- frOm them^ are at the same time so permanently fi that we are almost precluded, under the ordinary dm om res-ardme: the two as un ceptation of a " species/^ f doubted descendants of a common stock : and thus it is that insular faunas have frequently been magnified, in the novelties which they are supposed to contain, far beyond what is right. A person however who looks to the causes of things, and is prepared to recognize ejfects where there are fair grounds for anticipating them, will not be slow to perceive, that, in the small deviations I 4 4 4 4 I ^ i t J II ti} IT! m \ if"^ t •- - ^ ry n I I ^L I -J 4 i ! f t Ih i 1 * small islands are of course exposed to/aSd which would seem to have stunted the development (during a long series of ages) of the animal and vegetable worlds^ or from a diminution of area consequent on the breaking which we are so often accustomed under such circum- "1 ■t stances to behold^ the results of isolation itself (as an active controlling principle) may be traced out ; whilst geology, ever ready to lend a helping hand when ap- pealed to, will seldom fail to supply those intermediate links of probability which the believer in specific centres of creation must needs subscribe to, before he can draw any deductions on a broad scale, ' or be competent to r ^ analyse even the general bearings of a question thus necessarily comprehensive. Having thought it desirable to defer to a subsequent chapter of this treatise the few geological reflections which our subject may give rise to, it will not be my aim to allude to them in the present section more than is absolutely requisite. I propose rather to consider some of the ordinary effects of isolation, as mere matters of experience ; and to allow geology to tell its own tale when we come to examine the problem of self-dispersion^ r as occasionally interrupted by subsidence. If we except a few of the Heteromera and apterous Curculionid(By which appear to be influenced in a dif- ferent manner, the power of isolation over insect form is perhaps more especially to be detected in a deterioration of stature. Whether this principally emanates from the constant irritation of a stormy atmosphere, such as \ i I i iP ^ rv^= 7 ...u^ V /■^- i^ \) ^yV ^^- f1/ e. K3 *' # rf ^« m m r\ V iii k iti '^ ?i*^ V It'. W ^J r / "m *i ♦(■ % i ■-v . 72 up of a continuous land^ it is difficult to pronounce : nevertheless^ it is most consistent with both reason and analogy to suppose that each of those causes hai operated to induce a similar result ; and that we must s ■■> therefor%view them as working in concert^ if we would appreciate their action aright. It is a law^ to which a large proportion of the organic creation would appear to be subject^ that the exuberance of life (not so much, however, as regards the number of individuals which the various species may present^ as in the grandeur of their size) has reference to the magni- O ^-,w_ ' — . .. . — - ■ III o tude of_the spot over which it is permitted to range. The unnatural breeding-in of a single race^ which must of necessity happen unless fhe mtercourse with other varieties of its kind be possible, has always been attended with effects more or less peiTiicious ; and in the Annu- lose tribes I believe that the reduction of space which geological convulsions have at various epochs brought about, has been commonly succeeded {inte?^ alia) by a reduction of stature in those species which have been cut off from their fellows. I do not assert that there are rule times the above tendency. I hold it, however, as an absolute truism an anomaly. If, therefore, we were once to admit the latter to negative the former, no such thing as a law could exist. Hence it follows, as a corollary (unless, indeed, we are prepared to endorse that conclusion), that II « it 73 where there is a law there must be an exception to it ; and that, consequently, exceptional cases, if not exceed- from lerwise presumptive truth. TMs dwindling- down of size seldom to attract my attention, more or less, in almost every island wliich I have hitherto had an opportunity of exploring : space, however, will not permit me to dwell upon many instances. I have already adverted to the diminished stature Mshm M the first of which scarcely ever reaches, on that rock, more than half its bulk Mr. Holme College, Oxford, in like manner, captured the com- Calathus melanocephalus, Linn., and Olisthopus rotundatus, Payk., in SciUy,-the former of which mon seldom half, in length : and he also recorded, that the Bolito- chara assimilis, Kby, is im m those islands than it is in the neighbourhood of Penzance ^. The Vanessa Callirhoe, Pabr. (a geographical analogue of the Red Admiral Butterfly t. so common in our own * Trans, of the Ent. Soc. of London, ii. pp. 59, 62. t Considering that the true Vanessa Atalanta, of more northern latitudes, does occasionally occur around Funchal, it may be reason- ably contended that the fact of its coexistence (on the same spotj with the V. Callirhoe is strong presumptive proof that the latter is a true species, and no chmatal or insular modification of the former. And so, judging from a distance, and without local evidence to ex- plain this phsenomenon, I should have concluded myself : never- E 1 / i \ 1*1 ■■1 _ I A ' m I J L lS.. \ L L I I** bit ffl ,* |» 74 country), is permanently smaller in Porto Santo tlian it is on the larger, more Inxnriant and varied^ and there- fore more protected, island of Madeira proper. And, as regards the Ptini of that group, so completely are some of them ^^ affected by isolation, and hy exposure to a perpetually stormy atmosphere, that they do not attain half the bulk on many of the adjacent rocks that they do in the more sheltered districts of the central mass ; and so marvellously is this verified in a particular instance, that I have but little doubt that five or six species (so called) might have been recorded out of one, had only a few stray specimens been brought home for identification, without any regard having been paid to the respective circumstances under which they were found ^/^ That ^^one," Protean, representative is the 1 » *1i I4f HI Ml 4 ^1 4 t II theless, recollecting how easy of transport the larvse and pupae of Lepidoptera necessarily are (of which we have the plainest assu- rance in the almost certain introduction of the Pontia BrassictB, Sphinx ConvolvuU, Acherontia Atropos, &c. into those islands), especially in a region which for more than a century has heen receiving a constant supply of vegetables and ornamental plants from western Europe; I am induced to believe that the appearance of the Atalanta is a comparatively recent one, whilst that of the Callirhoe (which, unlike the typical Red Admiral, has naturahzed itself in nearly all portions of the group) must be referred to the remote period when migrations over a long-lost continuous land were in regular operation. The slowness of the change, in external aspect, which the isolation of insects from geological causes would seem to bring about (and which follows, as a corollary, if the above conclusion be true), I propose to discuss in a subsequent chapter of this work. * Insecta Maderensia, p. 260. I ■f ^ ) ^ i iLt-^ 1^ ^ .1^ < y •* - H i/^ *^^*V J ,^- ( ,i I ^ in point, that it may be admissible to quote, in extenso, a few of the observations which I have already pub- lished concerning it : C( commonest of the Madeiran most radiating-form for almost every island of the group, whilst, at the same time, the whole are so intimate connected together innumerable intern merge into each other) by them, in spite of the opposite contour of the m according as circumstances gulate its development Insta- bility in fact (in its broadest sense) may be considered most promment appears to be more members assumed commencing: with maximum com mass, the bulk elv intense. ' /3 IS likewise brightly smaUer. Now, if our premises correct, that locality and the action of the external elements have much •> e3 we have here to do,— as may be proved to a demonstra- — - tion by a careful study of its habits on the spot, where the influences of position and exposure are, in nearly all instances, more than sufiicient to account for the suc- a \%m k , I I tt'j fi \ I' I II < ■ -I J f I 76 " I-! f >4 I 44IH •fl intl #« M^e might have expected, a priori, that this state, from its peculiarity to the Dezerta Grande, would not only have reduced in dimensions (which it is), but in colour also (which it is not) . Here, therefore, observation, in situ, becomes extremely important ; since such does at once convince us that its almost exclusive attachment to Marianum every the interior of the stalks of the Silybum Grtn. (the Holy Thistle of the ancients), wit more protected portions of that island abound, affords it ample conditions, even on so bleak a rock, for its completion. Nevertheless, its stature (as ilready stated) is slightly diminished in spite of this : /md when we come to examine the individuals which infest the lichen of more* open situations (aberrant how- ever on the Dezerta Grande, and answering to the var. y. of the diagnosis), we immediately perceive that both of our required results are indicated,— the reduction not being limited to size, but extended also to hue. In Porto Santo this modification is the normal one, — where the msect likewise displays the same lichenophagous ui equally barren. But, if its maximum be attained m Madeir tions range throughout Porto Santo and the Dezerta Grande, it still remains for us to show where its minimum is to be obtained : — which, true to the modus operandi by LJectured desfrees to have been brought about, would seem to be centred Northern When ♦ i * lik / m\ f4l /' 77 ill mind tlie minute dimensions of that flattened rock, mucli depression, witHn its bounds, and is consequently seldom from from could ously subservient to atmospheric control should not have become materially affected, in its outward guise, through long seclusion on such a spot :— and accordingly we are not astonished to find the race which has been thus cut off for ages on this extraordinary little island, itself as extraordinary. It is indeed very remarkable to trace out how clearly the agencies we are discussing have here operated on the species under consideration, sexes (though especially the male) descend on tne iineo Chao to somewhat less than half a line in length, beijig for both some larger representatives of the Ptiliadce ! " * I stated above, that, although this diminution of accom amongst insects which have been long cut off from the rule to the result which has been described. We should re- member that immense periods of time are apparently necessary before any perceptible change can come over creatures from the stoppage of their migratory progress. in ^ V * Insecta Maderensia^ pp. 268, 269. 1) '^■'Wm !l ? ■m I »f mi fi f . 78 that in islands geologically recent (which often implies^ however^ their existence through epochs which would sound vast indeed to ears unscientific) we must not in- variably expect to discover evidences of this law. On the contrary, we must first of all take into account the age of their formation, before we can judge a priori as to the probability of its operation through a sufficient interval of time to have become conspicuous in its effects. I say ^^ through a sufiicient interval of time/^ because the process of deterioration may be silently going on^ even now^ in many an island^ ivhich has not yet shown any matured traces of its action^ except perhaps in the case of a few species which appear to be more particularly susceptible to contingencies from without. We should then call to mind^ that an enormous propor- tion of nearly every insular fauna is composed of acci- dental colonists during the last few centuries^ in which civilization and commerce have been unintentionally at work in the cause of animal diffusion ; and that, there- fore, if modifications in outward contour have not neces- sarily resulted during a positive geological interval, it would be absurd to look for them in the mere settlers (as it were) of yesterday. Thus, it will be perceived, how necessary it is to take every element and contingency into account before we venture to pronounce dogmatically on either the exist- ence or non-existence of any physical law; and how cautious we should be of denying the legitimate opera- tion of external influences in one region, because they Hi «* *4t t4 M *%U ^ •f i 79 would seem^ prima ft snxelv more the two, by tracing out (as may frequently be done) some us to understand the discrepancy, and to believe that same action may overruled sufficient time to bring its fruits to maturity. If a proposition be true, we should recoUect that it is always so (under all the circumstances and conditions to which it is appH- cable) ; for, otherwise, it would be both true and false,— if my the general tendency diminish become foUowi must remain disturbin; neutralize it. {£ When 3> says a writer of the last century, " hath hitherto constantly held true, or hath most commonly proved to be so, it has by this acquired an established credit : the cause may be pre- sumed to retain its former force ; and the effect may be taken as probable, if in the example hefi not appear something particular, tion^." Hence it is, that, even amoU; fi omena which one island may from nize the working of a selfsame law ; and clearly to detect, * Religion of Nature Delineated, p. 99. J^ ;■* !ii ^i'llfe I I / » > » n 80 from its failure results I •M ■gy 4tii( «W < U ft** » Ik M'. oiild wisb, come to pass. Tlie main object however of the present section being to show that a considerable amount of power is due to isolation itself, in regulating (after a long series of ages) the outward aspect of the insect tribes^ it is not strictly necessary that we should so rigidly insist on deteriora- tion of size as one of its primary consequences^ — since (whether it be so or not) we are merely concerned here to demonstrate^ that its influence^, in some shape or other is absolute and real. After the above remarks^, we shall not be surprised that the phsenomena displayed in certain islands^ as regards size^ are sometimes (though I believe it to be an exception to the ordinary rule) the exact opposite of what we have been describing. Let us not however be alarmed at this fact, on the bare statement of it, though the proposition which we have been lately ad- vancing were at once disproved ; since we shall find, on inquiry, that the case is not so desperate as might be imagined; and that in many islands where even this principle is to be detected, we may recognize traces of the other also. But how, it will be asked, can this be ? for, since the influences are the same, creatures simi- larly exposed to them must be similarly affected. Now although, on a broad scale, such a notion contains much n III (gii -ny ^ - «l -\ , 1' I 411 » i 81 + presumptive truth, on a narrower one it does not ahvays apply ; for species are differently constituted ab ovo, and will sometimes of causes wMcli are identical. Moreover, there is a remarked in most that the wings (especially the metathoracic ones) of their insect inhabitants are liable to be retarded in their development,— often indeed to such an extent as to illy evanescent : and I believe it to be a law that when any particular organ is either become Nature stunted or taken away, the creature receives a compensa- tion for its loss either by the undue enlargement of some / bulk such be the case, the presence of two apparently con- somewhat more intelligible ; nevertheless, on the above hypothesis, the specimens which increase in dimensions should un^ more diminish winged. And hence we arrive at the question, is this so ? My own experience would certainly tend to prove I ■ » * Although the result of a primary (or creative) adjustment to special circumstances, rather than of a secondary adaptation brought about by a self-modifying capability; we may ]ust call attention to the fact, that most of the blind insects, whether asso- ciates within the nests of ants, or natives of subterranean caverns, have either their palpi or antennae anomalously developed, as though, partially (although how, and in what degree, we cannot possibly ascertain), to make amends for the inconvemence which a total want of sight must necessarily entail. I > \aa^^ »^ i J i . • / cl t ^- E B "io , If # « 1 i . — u 1 > .-.-' iH^ u r m it .'. I V ':■ -I I m it ' ^\1 » IM y t A^ Il» \ ft \^ 'V x 82 that it is; and I suspect that future observations will confirm the fact. Meanwhile^ I must content myself with simnlv advancinp- thp, snhippt fnr nnnairlpv-i+ii^Ta oT^/l with will permit, and which occm* me almost spontaneonsly. Madeiras more than nsnal control over the alary system of their insect population ; for^ out of about 550 species of Co- leoptera which I have hitherto met with in that group^ nearly 200 are either altogether apterous^ or else have perfectly may our preceding conclusions (from the hyp thesis) be correct^ we should a priori anticipate an in- bulk of it. greater representatives are now^ through the submergence of the once surrounding continent^ endemic^ so that we have means wmgs is to be referred to the long action of Madeiran influences'^ or whether they were thus created severally This is cei-tainly rendered probable, however, from the fact that a large proportion of these apterous species are members of genera which are usually winged,— such as Tarus, Loricera, Calathus, Olisthopus, Argutor, Trechus, Hydrobius, Ephistemus, Syncalypta] Phlceophagus, Tychius, Longitarsus, Chrysomela, Scymms, Cory- hphus, Helops, and O^Am^,— whilst the knowledge that, out of i ^enty-nine gene ra which I beheve to be endemic in those islands, six only are winged (the remaining twenty-three being apterous)^ * ' il k m ■ \\ N* ^ H t W k 83 in the beffinmng; : and, for tlie same compare them mil this partial organic decay to be the consequence of their isolation on these rocks, whether their general stature has been subsequently augmented or not are some few, out of the 200 just alluded Still, there common appear to liave obeyed the principles to which we have h^-m^T^^^^ attentionJUsjwliiireasom to suppose, that many of the others (could we but behold them as they formerly were,— emi id) would be foui I alluded, in a previous section; to the DromiMS Dufts in Madeir result and isolation ; and I also stated that it was not always possible, whilst dealing with physical agents which are T,pnP.sarilv obscure, to refer the respective phsenomena may be), which would seem from \ Hence answerable for the changes which that insect has under- gone, I may here suggest that it is, in aU probabHity, to isolation that we must mainly look, if we would under- stand those changes aright. But what are the distinctive will not tend to dimmish the probability that there is something pecuhar in the action of Madeiran influences generally on the alary system of the insect tribes. ^ / r } I $if 11 Hka I / J !■ t i w fi* W .1. \. 'v* V ^ 1 f ItH: IV \ , ^ U 84 features, it may be asked, which the B. obscuroguttatus has adopted, since its first arrival from more northern latitudes over an unbroken * continent ? It has not altered much, after all : it is, however, the nature of the alterations, and their constancy, which give them their real import- In a few words then, the insect is rather larger ance. European ■ I omit other minor differences) its wings are evanescent. But this, on our above hypothesis, is precisely what we should have expected : for, since it is self-evident that the species cannot have been naturalized accidentally on these mountains, and since geology informs us that a vast interval has elapsed since the Madeiran islands were portions of a continuous whole, we have at once a suffi- cient time assured us for the modifications to be com- pleted, and to appear at length permanently adjusted in accordance with the conditions and influences which locally prevail. There are other examples which might be quoted in support of my theory,— that isolation, when involving a sufficient period of time, has a direct tendency either to * T do not think it necessary to apologize for the apparent dis- posal of this qucestio vexata ; hecause, from the wildness of the upland ridges to which the D. obscuroguttatus is in Madeira ex- clusively confined, I deem it an absolute impossibihty that it could ever have been introduced, through any chance agencies whatsoever. And hence, unless we reject the doctrine of specific centres m toto, I contend that it must have migrated, together with other insects similarly circumstanced, by ordinary means, and without natural impediments, from its own area of diff'usion. V v- L- > I C k V I \ / } ( i* ^1 )i / * '■ w^ t M : 1 1^ M / .^ jU.^ r ) Ut>. /■'■ / -'•^ f I f \ 1 * i-. J.*- m ( \ m ! ■■■; I 7Z - ' -i -r I— -n J" 4 r I . f u J- 1 J ^ i i i 86 from a transition state ?— an idea which the smallness of its wings, as compared with those of its British analogues, would seem rather to corroborate. stature generaUy to accompany that gradual extinction of the powers of flight ivhich isolation is apt to induce, it follows, on the other hand (as indeed I have lately wings without tive destruction, be taken from it, the primary efi'ect of isolation,— namely a diminution of bulk,--will for the most part happen instead. As this fact, however, has been already commented upon, we will not discuss it , afresh. Why it is, in the Insecta, that islands^ should nrp. more not easy to speculate. Mr. Darwin has indeed suggested, and with much apparent reason, that, were wings fally developed, the indiscriminate use of them might lead to unhappy results, by tempting the creatures to venture too far from their native rocks ; and that, therefore, this wise ur insular during heavy * I am informed by Dr. Hooker, that the only two insects (belong- ing respectively to the orders Coleoptera and Lepidoptera) which he detected in Kerguelen's Land were wineless. i (i J I:-, I J r ^\ \ f E I I I r f ' I I F 87 should in reality be gifted with them Mr inomena Eormy iwn fdlness ; and, furthermore consideration (though it unquestionably contains much presumptive truth) does at all interfere with the admission of it^ — seeing that either requirement may be fulfilled, according to the nature of the several species which are destined to be acted upon. Th IS, if flig number ptera, and beetles of a flower-infesting tendency, we shall f — ■• f ♦ .. "vniii am means certain) , and that the effect of isolation is more diminution of stature. But if, contrary aerial progression for their sustenance, as in the pre- dacious tribes generally, especially those of nocturnal habits, the reduced area in which they are confined, in conjunction, it may be, with the danger to which they would constantly expose themselves by the promiscuous employment of organs which their modes of life do not positively need, would seem to render the presence of wings unnecessary; and they are accordingly, by degrees, removed :— in which case, however, a compensation for the loss is not unfrequently granted by an increase (more bulk f ^ f A 1" V * ! K. V H^i \\ i +■ ' i ^ \ / i " .J9 m\ »«•■•» ^ *C .1 - 1 W( ■a, i.-' ^* 1, ' > '3 88 Madeiras I stature, accompanied for the most part respectively by the retention and annihilation of the powers of flight, is singularly traceable on the selfsame rocks, particularly the smaUer ones of the group. Thus, on the Flat Deserta, or Ilheo Chao, the Scarites abbreviatus, KolL, i WoU Helops WolL. finds its minimnm development^ — scarcely exceeding in dimensions some of members The Deserta modifying 'wn Notioph WoU planatus, KolL, OIisthopusMaderensis,Wo\l.,Caulotrupis conicollis, WoU., Laparocerus morio, Schon., Omias Wa- terhousei, WoU., Helops Vulcanus, WolL, and the Ellip-- sodes glabrafus, Fab., being also larger on that rock wi NotiopMlus apterous. r'- results apparent Take colour^ for instance ; and we shall per- ceive that in the Dromius sigma^ Rossi, it is sensibly affected. The normal state of that insect ''does not occur at all in Madeira proper, but only in Porto Santo. True it is that the modifications in the several islands present but slight differences inter se ; nevertheless beine: constant, I would lavnarticular strpas nr»r.n +i.^tv. I i I I r 1 :j=_l- ^' _ _^_ It f f \ m^ i^-f, ,'^ r ^ W*^-^ ■' ;^ J V \ - \ pj f ^l^^ I ^ / / n ^ > ^ / f "'^;/ C 89 very 7- form are even more ant, if possible, than those of latitude. That this is ar from facts minute many specimens my observation from Europ otherwise believe, under all circumstances, its thorax. Now, whilst this (we may almost character obtains in Porto Santo, in mmaculate Madeira it doei invariably infas cate in the centre; and on a small adjacent rock (the Ilheo de Eora) it is entirely dark. Nor pose that detaHs apparently so trivial are beneath our result markiii; development according to the circumstanx^es of the several localities in which they obtain, that we are alone im wider and geographical sense, a correct estimate value"^.^^ Maderensis, WolL, is much paler, larger, and more opake, on the Dezerta Grande Madeira great change which it has undergone through a long isolation on that rock, '' that, had the case been a solitary one, I should not have hesitated in regarding the specimens obtained from thence as specifically distinct ; neverthe- * Insecta Maderensia, P* 6- I liKM n f.. I \ :^f>H ^it ■ -, IkJi k\ i ^1 h n -.i - i i V*^. ^. -r ^ f *\ ^ ''^- -r t H 4 V .:i ^T 1 '\. 'I. J v.. -I 5 -*>> I v N ■■W 4 W Nt *t^ 90 .> oii J .:^ less, with the knowledge both of the modifying effects of isolation, and also of the kind of modification essentiaUy peculiar to that island, I am perfectly satisfied that it is a mere local state, although a very remarkable one and ^ i J.S t^ - --I ^4. -1^^ -r *■ .-^ -■*- . J. The 'Wl Maderensis, WoU brassy tinge in Porto Santo, and much acuminated in front; whereas on the Dezerta Grande it is almost mvariably copperi/, and less narrowed anteriorly. The lucifugus, WoU (C ;ure every appears to possess a slight modification for island of the Madeiran Group : and hence small «uaues of difference, which might otherwise be regarded as trifling, become directly important, and cannot be ■even though a general col- faima may deem it unnecessary In real fact, however, such distinctions, when viewed geo- pphically, are of the greatest interest, as serving to illustrate what we have so often had occasion to com- ment WoU formf/^ The Psyl- Madeira (( testaceous. with the Madeiran That the species is identical, however colour undergone * Insecta Maderensia, p. dQ. t Id. p. 310. \ V It I I 1 i t k 91 com 4 The Scarites ahbreviatus, KoU., occupies the loftiest peaks of nearly Madeiran dant over the entire ancient continent, whatsoever its limits may but an isolated part. " There are traces of it in the Canaries, from whence occasional specimens have been brought, and which, from the want of local data and of sufficient numbers to reason upon, have in their turn been severally regarded as distinct. The fact however is, extreme assumm; ;ure the circumstances of the spot on which it is isolated. careful many minute will Madeiran For it is impossible to snppose that every rock contams its own species, that is to say, lias had a separate creation ex- pressly for itself, are of a conclusion at which we must small and even constant differences !ific. Eej ecting therefore this hypo- thesis as utterly untenable, and as contrary to all expe- rience, we are driven to acknowledge that isolation does, in nearly every instance, in the course of time, affect, more or less sensibly, external insect form;--which being admitted, we have at once an intelligible principle * Insecta Maderensia, p- 452. (tt i til \i »H » !■■ m u ? |i m III 1; i I I 92 account of which, when viewed simply as a difference, indepen- dently of the circumstances producing it, might have been regarded as sufficient to erect a ' species ' love of truth^/' multiplyin upon Such are a few of the circumstances, influences, and conditions, by which the outward aspect of the insect tribes is liable, within definite limits, to be more or less regulated : and it is impossible to view them with an unbiassed mind and not arrive at the conclusion, that physical agents generally have a very decided control contour In selecting the examples which we have lately discussed, I have avoided as much as possible those startling in- stances of variation which distant quarters of the globe wil naturalists m New Worlds. I have therefore contented myself with such data as must fall * 1 1 • Wl the principle be allowed in the one case, it cannot long be objected to in the other. There are few entomolo- gists who would not recognize, in the abstract, a legiti- mate capacity for adaptation in every insect with which * Insecta Maderensia, p. 11. { i ht 93 modificat , many, who, as tlie fixed disturbances from them The col- lectors of the present day are so prone to regard every permanent difference as a specific one, that a large pro- portion of them do not sufficiently realize, that well- marked races, or states, are no longer matters of hypo- thesis, but of fact; and that, therefore, a sensible amount comlDinat: but even anticipated and looked for. Such however would cate a greater latitude for geographical influences than admitted by many Especially more omen a, for i am seldom, if ever, made for the qualify isolation, per se, most conditions which we have attem pages to examine. ic rerum causas '^ is a motto which the student of Nature i stantly in view ; for it is undoubtedly a task to discover the reasons for what we see, than the more mere He into the everyday circumstances around him will be ^ ■ - m II J I A- item comes within his ken, to chance ; for to him the whole I [I II i«it m n k ft; ^ r 94 system of created thingi with design. Natura i wi true Let us not therefore be discouraged at the apparent smallness many of our be drawn, for nothing is in reality trivial which is the Wl; mves unim Nor may discoura; conflicting phsenomena, and detect in each a primary controlling cause. We should obscure various only, on a broad scale that we can look for imiformitj of action, even jfrom conditions which may appear to be identical. a Nature is not irregul because there are some seeming deviations from the These are generally the effects of that rule have upon natural productions^. circumstances ^^ * Religion of Nature Delineated, p. 84. ^ 1 I 1 \ I ^ , / 95 1 I 11 ( I ti \ /« CHAPTER IV. ORGANS AND CHARACTERS OF VARIATION Having in the preceding chapter briefly alluded to some of the principal causes by which the outward aspect of tlie insect tribes would seem to be in a large measure (tbough witbin definite specific limits) regu- lated^ it may perhaps be desirable to gather into a small compass^ from those remarks^ what the chief organs and characters are which appear to be more peculiarly beneath the control of the various influences which we have been just discussing. To imagine that r w^hen an insect has become much altered in its general contour^ all the parts of which it is composed are equally affected^ is contrary to experience ; since obser- vation warns us that there are but few actual members which are capable of change^ — whilst even the external features^ or secondary diagnostics^ are only interfered with according to a fixed law^ the workings of which are necessarily modified^ in proportion as the constitutions of the several animals are difierently organized and acted upon. As regards positive structure^ indeed^ we can have but few observations to communicate^ — seeing that the limbs and appendages themselves are usually of so con- )■: f!i I I tm. v^ J iv ^ 96 lat disturbing tliem from tl Still, would from from with out : tlie number of the antennal joints, for instance, in ultiarticulate may « . • am The con- nateness of the elytra, again, is a character which we may and this I have myself noticed, at times, to fluctuate, according to the circumstances and conditions of the respective localities in which the particular species obtain. Such Hi H. vividus, Dei.) of the Madeiran Speaking of this peculiarity, in my volume on the Coleoptera of made haps its most singular character, and in Avhich it diflPers from every other Harpalus with which I am acquainted, consists in the tendency of its elytra to become united or soldered together. I say ' the tendency,' because it is not always the case that they are j oined (which. more remark most much shore they are. I have examples, however, from the upper as well as the lower regions, in which both states m *l I 4 PL U4I I %u 97 ji|ii4H \ are only partially connected^ being free at the apex though, firmly attached towards the scutellum. In every instance^ however^ even where they are nnited throughout their entire lengthy a little force will succeed in separating them^ showing their structure^ as I have indicated in the diagnosis^ to be sub-coimate rather than connate. But that it does require force to effect the dis- junction^ when they are really in the condition described^ is proved to a demonstration to any one who has seen the remains of the insect beneath the slabs of stone on many of the small adjacent islands where it most abounds^ or drifting about over the surface of the rocks^ ■under which circumstances I have observed them in immense numbers^ apparently the accumulation of two or three generations^ which the violence of the elements had not been able to sever. It is rare in the sylvan districts to find them joined; nevertheless such is some- times the case^ — thus proving that the peculiarity is not actually essential^ but merely one which it is the ten- dency of the species to assume^ and which is more developed in some specimens^ and under certain condi- tions^ than in others."^ " But by far the greatest amount of variability to which insect structure is liable^ is presented by the ivings^ especially the metathoracic ones. The wings^ indeed^ unless I am much mistaken^ are essentially (as compared with other primary details) organs of variation^ capable of being more or less developed^ according as the several * Insecta Maderensia, pp. 56, 57- r I % 4 DKi i» r r !l Wm * litm ■w fl 1 m% 98 II J 1 are tate tlieir action. I will not recapitulate tlie evidence whicli I tave already adduced, proving that islands liave an especial capability of their own, either for increasing or neutralizing, as it may happen, the powers of flight (in which latter case, however, a compensation is usually made for the loss) ; but I will point to the data which are there brought together, in support of the hypothesis for which I am now pleading,^believing that they will be found sufficient, on inquiry, to establish the doctrine of alary mutability, so far at least as it is connected with isolation as an element of control. If, however (irre- snectivelv of its cause) , the thing itseK be recognized, the principle is at once established; may matter ensure this concession or acknowledgment, the occasional proneness to variation of these thoracic appendages is, as a law, admitted. The only que would * themselves circumstances do they principally should it hapnen that organs which ^ ) ^) ^\ SO necessary a medium of subsistence, should m^ in reality in the preceding chapter. Nevertheless concerned, it is in maximum "^ which the wings of the Insect a are liable, and that it is in seasons of extraordinary heat that their development :^ ^^ i I, m o '^..%^ u JO aJi<- ii f> ,}r a-if^ cu r% K £^ •J- c/^^ i*"*-' ; U 7 f,^ ^ '\ / U^- *> XriM-- srywhere inclined (if* will to state, that in continents, when any decided alteration most comes result the species are not absolutely dependent on aerial pro- gression for their food (in which case, in order to prepare for the contingency of being blown out to sea, the capacity of the wings is commonly augmented), the reverse is nearer tlie truth. So that the second problem, the reason why appendages thus apparently essential should be subject to inconstancy, — is at once rendered from ►yment would be ant to brin trouble that (when not an actual sine qua non to their existence) they are liable to be taken away j whilst, even in recom pense. Mr, Westwood, in his admirable Ini Modern Classification of Insects^ has instances of alary variation; which, however, as he does recorded many not appear to pecul; faunas, are principally in corroboration of what I have just insisted upon as the usual tendency in continents, ■namely, an enlargement of the erratic powers. Speak- ing of the Aphelocheirus aestivalis (a member of the f2 ^ /t/ t U'l I * i i 100 Hemiptera)^ lie observes : ^^ My British specimens have but shortj rudimental^ oval hemelytra^ like those of the bed-bug ; but I possess one of Bosoms original examples^ described by Fabricius^ not quite so large as the others^ in which the wings are fully developed. I do not^ how- ever^ on that account^ regard the former either as pup?e or distinct species^ but as undeveloped specimens in the imago state ^/^ And whilst discussing the Hydro- metrid(Sy he expresses himself thus : ^^ It appears to me^ that^ from causes of which we are ignorant^ numerous individuals of many of the species of these tribes are subjected to an inferior kind of development in the imago state^ which does not allow the acquirement of wings^ — which^ however^ in certain cases^ acquire their full size. Hence^ I consider that the apterous specimens of Hydrometra stagnorum^ those with very short elytra^ and those with the full-sized wings and wing-covers^ are all in the imago state^ although some are more perfect than others t-^^ And^ again^ in his reflections on the Hemiptera^ Mr, Westwood says (and most entomologists are aware of the fact) : ^^ The species of Gerrisy Hydrometra, and Velia are mostly found per- fectly apterous^ though occasionally with full-sized wings. ^ Chorosoma miriforme^ Prostemma guttula^ Pachymerus brevipennis^ &c., are generally found with very short wing-coverSj but sometimes with ftdl-sized wings J /^ In like manner^ the Cimex apterus, Linn, (one of the * Introduction to the Modern Classification of Insects^ ii. p. 466. t Id. ii. p. 469. X Id, ii. p. 454. i i 101 Lygmidoi) '^ exhibits, in an eminent degree, the ordinary occurrence of an imperfect perfect-state; whilst indi- viduals are occasionally found with fully developed organs of flight ^^> Lyceus bi^evipennis^ Lat., also ordinarily occurs with abbreviated hemelytra; but it has been found with them perfect by Westwood, as well as with metathoracic wings. None of the above examples however would appear to do more than refer to the alary instability of the Insecta, as a matter of fact ; but this is aU for which we are now contending, — the preceding chapter having been in part devoted to some of the presumptive causes of it. Whether the specimens of Oncocephalus griseuSy to which Spinola called attention, were insular ones, I cannot say ; but he seems to have noted an example in which an opposite phenomenon to those which Mr. Westwood has cited, was displayed, and moreover to have speculated on the conditions producing it, when he suggests : ^' L^influence du climat septentrional parait avoir arrete le developpe- ment des organes du volf.^^ And, again, when com- L menting upon the other tendency in a representative of the Reduviad(By he says (^Essai,^ p. 96) : ^^ Je pense que la presence des ailes et leur developpement dependent du chmat.^^ Whilst treating of two British species of the same family, Mr. Westwood observes : ^^ The Pro- stemma guttulay Fab., and Coranus subapterus. Curt., are interesting on account of their being generally found in * Introduction to the Modern Classification of Insects, ii. p. 480, t Essai, p. 103, ^ i \ ttF ^j ■' ■ timn ■* ^^^ 3r 4. / 102 an undeveloped imago state^ — the latter being either entirely apterous or with the fore- wings rudimental^ although occasionally to be met with having the fore- wings completely developed"^/^ The common Phos- phuga atrata of our own country has the organs of flight very rudimentary^ and much too small for use : yet the late Mr. Holme of Oxford has mentionedf^ that he has several times taken it on the wing^ during the hot sun- shine. And, concerning the Olisthopus rotundatus, he specimen SciUy more such as we may trace the counterpart of in higher ani- mals than the Insecta. Mr. Gould informs me^ that the which have but a comparatively ss over^ to the African continent^ specifically identical with them) a Swallows Malta I distinct race from those of England^ — all of which^ he believes^ winter in Morocco. But^ what are the differ- ences displayed ? From amongst many minor ones^ of a climatal or geographical nature^ the most conspicuous is the length of the wings ^ — those which have annually a longer journey to perform havings through a course of ageSj acquired^ as a race^ a superior capacity for flight. And^ in answer to a late query on this subject^ he adds that all the sylvan birds in Malta^ such as the Black- caps^ Willow-wrens^ &c.^ though unquestionably of the ■ t * Introduction to the Modern Classification of Insects, ii. p. 4/3. t Trans, of the Ent. Soc. of London, ii. p. 60. J Id, ii. p. 59. w 3 y-H 103 4 same species as those of Great Britain^ exhibit small local characteristics by which they may be immediately distinguished^ — such as the length of the wings^ size of the billsj and tints of the plumage. So that the migra- tory birds generally^ which pass to and fro between Europe and Africa in that particular latitude_, would appear to form separate races from those which traverse the ocean to our own country; and to be^ most of them, remarkable, inter alia^ for a slight shortening of their organs of transit. If, however, the members of the insect tribes are capable of but small variation in actual structure^ with the exception, in certain instances, of the greater or less development of tlie wings ; we shall find that their ex- ternal characters are much more prone to instability^. There is not an item indeed of all their secondary^ ^ y diagnostics which does not admit of a positive change ; and, though it be only within fixed limits that the several modifications can occur, those boundaries are frequently far apart, and include at times numerous phases within their embrace which have been too often looked upon as specific. Thus, whether we regard their J bulk^ outline^ colour^ or sculpture^ anything like absolute r constancy, under all circumstances and conditions, does not so much as exist ; and we are driven to admit, that the physical influences to which these various creatures are exposed have a very decided power over their general configuration and aspect. It would be needless, however, to attempt to discuss the above details of aberration ftPnnrf^f.plv : because, where anv one of them is esneciallv i« IK) '' ft 1 11 111 li 104 interfered with^ it usually happens that the others are more or less involved with them : but we may offer a few desultory remarks^ which will tend to show that disturbing agents are apt to mar them both individually and as a whole^ — and not only so^ but to affect them in a permanent manner (as indeed has been already inti- mated)^ according as similar combinations of them are^ from local causes (as it were)^ selected^ to be acted upon. I have stated in the last section of the preceding chapter that insect stature is eminently beneath the control of contingences from without; adducing^ amongst other examples^ in support of this^ the Madeiran Ptinus albopictuSj — a species which^ whilst it averages more than a line in length on the central island of the group^ is reduced to less than half that bulk on a small and weather-beaten rock (the Ilheo Chao) at a distance from J ■ it. Judging indeed from many hundred specimens of the Ptini which I have submitted to a close comparison, ^^ the most constant of their characters would seem to be outline and sculpture, whilst size and colour are appa- rently the least to be depended upon : — so that trifling differences may be of specific indication in the former case, where in the latter much larger ones are worth- less"^/^ I have in fact generally noticed, that size and colour are more peculiarly liable to be affected together. This, however, is nothing more than what we should anticipate, since the same causes which have stunted the \ * Insecta Maderensia, pp. 260^ 261. -1^ 105 dimensions^ dnring a long series of ages^ of any par- ticular creaturcj will for the most part be found to have also impaired the brilliancy of its tints. Luxuriance of vegetation and sheltered districts are alike conducive^ in the Annulosa^ to the development both of the body and its adornment ; or^ in other words^ where the vege- table creation attains its maximum (which it certainly does not do in situations which are exposed to the irri- tating consequences of a perpetually stormy atmosphere)^ there the animal world will be usually observed to thrive. There are many insects which appear to have disthm Lstates, \io\h in ma seldom (in some instances^, I believe^ never) able to unite by intermediate links^ or grades; and yet which are universally admitted^ although found in actually the self-same spots (a fact which prevents their being looked upon as separate^ local modifications of a common type)^ to be mere varieties of each other. They are^ however^ exceptions to the general rule ; and^ although infringing on the strict definition of a ^' variety/^ as given at a pre- ceding page"^^ we nevertheless feel an a priori conviction that they are by no means specifically dissimilar inter se. Such phases^ as regards stature^ are presented by the our own melanocephaluSy Aphodius plagiatus^ and the Psylliodes er * Vide supra, p. 5. F 5 I i^ i. ■- ■ I I ' ^i;^ j« ^ y 'f ei t| ■ Ml 1 I 106 , Mshm) may be quoted^ as cases in Madeira^ tlie Mycetoporus pronus, Thus, small form, livins: in communion, — wMcli I un questionably identical (differing in no respect except in size) : and so have the Stenus Saprinus nitiduluSy Fab.^ HeerL WoU ms insect tribes, when subjected to the action of certain from wi much m. \ / ^ •r 1 * Although, in our ignorance of their real nature, we cannot cite them as actually analogous to these separate phases in certain members of the Insecta, yet we are forcibly reminded by the latter of the distinct states which many of the Terrestrial MoUusca pre- sent (frequently in equal proportions) in the same locahties. Thus, \ most of the Pupce have at least two abruptly-marked forms,— a larger and smaller one. Many of the Helices also exhibit this ten- I dency in an eminent degree : I have indeed been shown specimens by Sir Charles Lyell of the Helix Ursuta, Say, from North America, one state of which is considerably more than double the dimensions of the other ; and I believe it is a well-known fact that intermediate links have not yet been observed to connect the extremes. May not therefore the gigantic H. Lowei and Bowdichiana, which are now extinct in the Madeira Islands, have been but forms of the H. Portosanctana and punctulata, respectively, — co-existent with them, though more sensitive to the great diminutions of altitude and area which were consequent on the breaking-up of a once con- tinuous land ? If such be the case, however, it is certain that they were far commoner at an early period than their smaller colleagues (which, now, in their proper districts, absolutely teem), — seeing that the latter are extremely rare in the fossil deposits, whilst they thpTHSplves literallv abound. ? .1 f 107 F that it is unnecessary to repeat it here. True it is that it was then my sole province to discuss the causes which would appear to regulate^ in a large measure^ the external aspect of the Annulosa ; yet the existence of inconstancy^ in the several organs and characters involved (with which alone we are now concerned)^ was^ by the nature of the case^ implied : so that if the disturbing element was de- monstrated^ the mere fact that the thing (whatsoever it may have been) was interfered withy was surely proved a fortiori. I there pointed out the great proneness to a change in hue which divers circumstances are apt to induce; and I particularly instanced proximity to the sea-shore^ and other saline spots^ as weU as an attach- ment to calcareous districts^ as amongst the most power- ful of the deranging contingences. In case, however, that any further evidence should be looked for, on this immediate subject, I will quote the following, — ^relating to the Bembidium Atlanticum of the Madeira Islands, which was but just touched upon in that chapter, — as a >le of the general effect of physical agents on the colour of these lower creatures. ^^ Through- out all the Madeiran Coleoptera there is perhaps no insect which displays such an extraordinary range of colouring as the present one does ; and although it is true that the section of Bembidium to which it belongs is essentially a variable one, yet I am not acquainted with any Peryphus in which the paler patches of the elytra are so remarkably unstable, or which appear to be so completely under the control of external circumstances, exam ^ ir *fi J J (m f ;■ y. ill :i w m m\ 108 as are those of the B. Atlanticum: and indeed unless mass many i) puts on between its extremes. examination careful consideration of tlie several localities and altitudes in me unquestionably but a single type of form amongst my entire series, since the whole are so intimately connected. colour im or to draw a line of specific demarcation between any of the chain. It wiU be per- members ceived, by a reference to the diagnosis, that the insect in from nearly a pure through a weU- defined spotted state, into one which has the elytra almost testaceous,— the paler portions being become almost to cover the entire surface. Madeira seem in Porto S anto the brightly coloured ones preponderate. and in fact are all but universal. Both extremes do nevertheless occur in both islands, the tendency being merely, in either case, to assume the particular modifi- cation characteristic of the spot"^. And so it is with the outline and sculpture (no less than with bulk and hue) : they also are equally Hable to disturbance from physical causes, as indeed has been * Insecta Maderensia, p. 78. ! I I 41 \ 109 already insisted upon. Like most of the minutiae of ■ * J * variation^ however, to wHch we have called attention, it is more particularly on islands that this is to be observed, — isolation, during an interval sufficiently long, appear- ing to possess some especial control over the external j contom- and surface of the insect races. Thus, in the Madeiras, for instance, the Caulotropis lucifugus has its prothorax more distinctly punctured, and its elytra more perceptibly striated, in the principal island, than on any of the smaller members of the group ; in Porto Santo, indeed, it is almost free from sculpture of any kind ; whilst its ally, the C. conicoUis, apart from being some- what larger, is, on the contrary, both more punctured ;\ „+^;„+^;i ^^ +i,q Tio-zov+ii Clvfir\(\p than it is in Madeira proper Wat 67 its shghtly increased bulk and less shining envelope, in that locality), is more lightly impressed on the Dezerta than it is in Madeira : and, not to mention other differ- ences, the Ellipsodes glahratus is densely beset with most minute granules on that same rock- the mountain slopes of tlie central mass ■wliereas on polished and glabrous. Helops confertus ilptured in the lofty regions of Madeira, than in the lower ones : H. futilis Madeira The Eury gnathus Latreillei assumes a permanent variety on the Dezerta, the insect having become modified through a long isolation on those weather- beaten heights, I 4ilk I * #p* i* Mir 110 where it not only attains a more gigantic stature tlian !».» a in Porto Santo^ but is invariably also more parallel and opake^ has the sides of its prothorax more recurved^ with the punctures towards the lateral angles almost obsolete^ and the strise of its elytra somewhat more evidently punctate"^. Such examples^ however^ might be multiplied ad infi- nitum ] and I will not therefore devote further space to the bringing together of facts which it is hardly possible will be disputed, — especially as it has been my wish, in the present chapter, merely to enumerate what the organs and characters principally are which are more peculiarly sensitive to change, throughout the Annulose tribes. This I may venture to hope, though briefly, I have in part done ; and I will consequently pass on to other considerations, which, even if somewhat alien to the im- miediate question of insect instability, should scarcely be altogether omitted in a treatise like this. * Insecta Maderensia, pp. 21, 22. mi t. . Ill t H > • CHAPTER V GEOLOGICAL REFLECTIONS. We freq-aently hear it asserted^ that^ since tlie members of the Insecta are so numerous and minute^ when com- pared with those of other departments of the organic worlds the entomologist^ whose province it is to collect and classify them^ can have but little time^ if he attempt the real advancement of his particular science^ for ge- neralizations on a broad scale, Now^ whilst there is necessarily some reason in this remark (for the investiga- tion of species is a work of such labour and drudgery r greater leisure hours comman should most observers ; and have^ many of them^ spent whole years of their lives as humble students in Nature^s domain. We need not be afraid that an occupation amongst what is microscopically small is liable to cramp the mind^ and render it unfit for wider processes of induc- tion^ since the very opposite of this would seem to come nearer to the truth. The understanding which has been well tutored by a system of close and steady obser- ■Ml I tir ■W 7 ^ !* iiip nm m-9 1^ I I 1 « 114 occult may fc dbility equally satisfied that this cannot by any logy. Let us therefore glance hastily at a few of those more undeniable convulsions which we are aware haye^ at various epochs^ taken place ; and endeavour to catch a glimpse of how^ in the common course of things^ that portion of the insect world would be affected which was exposed to their influence. First and foremost^ perhaps^ in importance^ of aU the changes which it is self-evident have happened^ may be mentioned subsidence. Including, as it does^ both the fe some tion of others, there are, I believe, no physical crises to which we could point, through the instrumentality of which very case, more existence of the insect races (not to diffusion) has been, by the nature of the riously interfered with. We know that there are certain species of an alpine and boreal cha- racter, which cannot live except in a climate of low tem- peraturcj — guaranteed to them either by elevation in one land, or by a higher latitude in another : and let us picture the consequences of the gradual sinking of a mountain chain, even to a small extent, the summits of which only just afforded the conditions of atmosphere necessary for the continuance of creatures like these. Now this is an example by no means far-fetched, and such as must have occurred in instances innumerable. But what would be the many results of a diminution in H ^# 115 the level of our imaginary range ? It needs no argu- ment to prove^ that one at least would he manifest in the total extinction of those forms which could not adapt themselves to the increased heat. Others^ which were able with difficulty to endure the alteration^ would in all probability^ even though they had now emigrated ■1 to the loftiest peaks^ flourish less vigorously than before ; and it is not unlikely^ moreover^ that they would become somewhat modified from their normal states^ — states which^ be it recollected (for this is an instructive lesson), would still exist in more northern zones. During my researches in mountain tracts, I have remarked teem My experience would certainly tend to prove, that, in a general sense, one or the other of these extremes does almost constantly obtain. And, although I would not wish dogmatize would movements will not afford some right interpretation of them. Be this, however, as it may, I can answer, that in many countries, where there are strong indications of the former, the alpine summits harbour an insect population to a singular extent ; whilst in others, where the latter is as distinctly traceable, the upland ridges are comparatively untenanted. Now we have already shown, that where the gradual lowering of a region has taken place, there will be, of necessity, an A \ If ^ i>iiii| V I f 'kI :M r \ 116 allowin Hfe on its loftiest pinnacles / tude for their development) to have perished, we shall have concentrated at ttiat single elevation the residue of all those which have survived from the ancient elevations above it. But^ if^ on the other hand^ an area, already peopled, be in parts greatly upheaved, there will be either a universal dying-out, from the cold, of a large proportion of its inhabitants, or else an instinctive striving amongst them to desert the higher grounds on which they have been lifted up, and to descend to their normal altitudes: in both cases, however, the present summits will display the same feature, — namely, utter desolation. Such are a few of the effects which elevation and would tested by theory and practice) to produce. It yet remains for us to suggest, that the latter, when canied to its maximum, so as to cause the actual separation by the sea of one district from another, is a contingency of ulatin distribution of the Annulose tribes. Their outward contour and aspect shown beneath the control of isolation, provided a suflacient ultimate absence from any particular ment which it offers to tb have not vet touched unon. ratory Let us conceive, therefore. / t / 117 an extensive continent ; and^ since the insects which at present inhabit onr earth must, if the doctrine of specific centres be true, have been originally created in certain definite spots, let us suppose a limited proportion of them Self- dissemination, we will assume, has been going on for centuries : those species which were gifted with quick diffusive powers have become pretty evenly dispersed over its surface ; whilst those of naturally slow or seden- com around the respective localities of their birth. Such may- have been the case, at some fixed period, amongst the aboriginal beings of any country which we choose to select as an illustration. But there is another element to be considered. If this region be not insular, it will from beyond its bounds ; and these, therefore, according to their several capabilities for progression, will have, like- .\ wise, in parts, overspread, or tenanted, it. Now it is impossible to cite a more simple example than this. But let us endeavour to realize what would be the neces- sary consequence of the breaking up of such a district as that which we have imagined. If a general sinking should take place, causing its higher points to be alone visible above the ocean, or merely 2^. partial one, so as to admit of the sea encompassing portions of it which would remam unaffected in their altitude; the result practically would be the same,— namely, the constitution of a group of islands out of a once continuous land. Then, as regards the -( '■^m ^^ mf^ !* m% J hi "I. I' . fc, ^ -jh 'I I. k 118 m animal population of this tracts the main phsenomena are almost self-evident. Should any of its isolated frag- ments chance to contain a portion of one of those limited areas which a species of slow progressive powers had would of course would now he defined as endemic. Numbers of these small areaSj or^ in other words^ of the species which had over- spread them^ would in all probability be lost for ever ; whilst the occurrence of any of the surviving ones in more than a single island would manifestly depend on the proximity of the islands inter se. Those forms which ^ had diffused themselves over the whole original con- tinent would now be found in all the detachments of the cluster; whilst others^ which had wandered over the greater portion of it only^ might be traceable perhaps in every island except a few. Such are the primary facts which suggest themselves^ whilst discussing: the question of isolation as reffulatinfir the distribution of the Annulose tribes. ifter effects on their external configuration and development^ we have examined in a preceding chapter of this treatise; and we have also lately intimated what might be a few of the presumptive consequences of a subsidence (in a general sense) ^ fi im principle of isolation. Before^ however^ we dismiss these brief and elementary refiexions on the upward and down- ward movements which geology testifies to have occurred^ at various epochs, on the earth^s surface, I shall ner- 119 + haps be pardoned if I digress so far from my immediate subject as to trace out some of tbe actual results of iso- lation in the diffusion of the Insecta (especially recogni- zable in the stoppage of a former migratory progress) in a few of the northern Atlantic groups. I should pre- mise^ however^ that it is from the Coleoptera alone that I shall attempt to draw my inferences; nevertheless^ since that order is more extensive than any of the others^ and has moreover been closely investigated in most of those islands, it may possibly afford us data of sufficient comprehensiveness and accuracy for practical purposes. To commence, then, with the Madeiras and Canaries ; the first facts which isolation discloses to us, concerning r the statistics of a region which was once continuous throughout that portion of the Atlantic, are the slowness and the direction of the ancient migratory movements. The former of these is rendered evident from the vast r number of endemic species which are at present con- tained, not merely in the two groups combined, but in the several islands of which each of them is composed. True it is, that these peculiar forms are, most of them, ■ L apterous, and of naturally sluggish self- disseminating powers ; yet, still the circumstance remains, that these various creatures had not overrun areas of any extent before the land of passage was destroyed, — for otherwise they must have occurred,. now, on islands and rocks but slightly removed from each other, which they do not. The latter of the above conclusions, namely, the direction of the miffratorv current, will become apparent in the , f > ' / ' 1-^ m i . f ii: itim \ • I \ m nm I* £■' ,A V V ] 120 sequel. We may premise however^ that^ so far as the aborigines of this province are concerned^ their course -will be foundj upon the whole^ to have been a northerly one. As regards the slowness^ and the direction^ of the quondam migration (questions which can scarcely be treated apart from each other) ^ some light may be thrown on the subject from considerations like the fol- lowing. The Canaries are the head-quarters of the genus Hegeter ; Teneriife may indeed be called the land of Hegeters. No less than thirteen or fourteen species have been recorded as indigenous to those islands j and there can be no reasonable doubt whatsoever that that ancient region (when continuous and entire) was the primaeval centre^ or range^ of that Heteromerous group. The Hegeters are an apterous race^ and of a sedentary temperament ; hence^ when the area (whether by general or partial subsidence^ it signifies not) was broken up^ it r is not surprising that those local fragments of it should have become the nucleus of reception^ as it were^ for the members of that genus. Nevertheless^ a few of these many representatives (of more discursive capabilities per- haps than the rest) had found their way^ before the period of dissolution^ to a considerable distance from their original haunts. Thus^ one of them (the H. late- bricola^ Woll.) had arrived at what now constitutes the rocks of the Salvages ; another (the H, elongatuSy Oliv.)^ at least_, if not two^ had colonized the Madeiras^ and is said (though I believe incorrectly) to have even reached 131 the present coast of PortngaL This latter species is more much as it has^ also^ naturalized itself (though this may be a more recent^ and accidental^ circumstance) on the opposite shores of Africa. One rate manifest, — that the He2:et thin ^ — that the Hegeters attain their maximum in the Canaries^ and that a few members only have been sent off^ in a northerly^ or north-easterly^ direction, from thence. In like manner, the genus Tarphius is distinctively- Madeiran. I have detected nearly twenty well-defined species of it in that group; yet, out of so large a number, two only have occurred beyond the central ^ island. Now the Tarphii are, also, wingless; and crea- tures of very sluggish propensities, — scarcely ever stir- ring from the masses of loose rotting timber which they so assimilate in hue, and to the under sides of which they affix themselves, day and night. Although difficult to investigate in their precise economy, it is extremely probable (may I not say, certain ?) that some important and peculiar office is assigned to them in the remote upland districts to which they exclusively belong : and there cannot be any question^ to a person who has studied them carefully on the spot, but that the region which they now inhabit is the actual area of their prim- aeval appearance on this earth. Many kindred species may of course have been lost, during those gigantic subsidences which caused the Madeiras to be shaped out, and to teU their tale above the waves as ruins of an G J 'IM V) \ mfi i'-\ K* ^ 123 ancient land ; yet our existing cluster of forms could not have wandered far at that early period^ from the Serras and ridges of their birth^ — perhaps not so far indeed (considering the limited bounds within which they are now confined^ and that time should in reality have increased their range rather than diminished it) as they have succeeded in doing at the present day. Hence we may reasonably conclude^ that Madeira proper is an example of what we have alluded to in a preceding page_, -namely^ of the accidental retention^ during a vast downward movement^ of a nucleus of small specific areas of colonization^ the colonizers of which had not extended elsewhere. But I stated^ that two of the above-men- tioned Tarphii have occurred beyond the central mass. It is in Porto Santo that they make their appearance; nevertheless^ since one of them is apparently peculiar to that island^ it is only the T. Loweiy WolL (an insect of a different^ and more active^ nature than the rest) which has violated that local ewclusiveness which would seem to be almost a generic character^ as it were_, of its allies, at species^ however^ both in its manners and aspect^ recedes materially from the remainder. Although^ like them^ nocturnal in its habits^ it is able to run with con- siderable velocity ; and^ instead of attaching itself to the blocks of putrefying wood^ which both fall and decay in situ on those elevated tracts^ it hides within the bunches of Evernia scopulorum and prunastri which clothe the trunks of living trees^ and fill up the crevices of the weather-beaten peaks. Hence^ when contrasted with \V I r 123 L its comrades^ we can easily understand how the varied processes of accidental transportation would operate to increase the range of a creature which differs so essen- tially^ in many respects^ from them. It is indeed^ not unfrequently^ brought down^ at the present day^ by human agencies from the mountain- slopes j for^ since the cutting of faggots is one of the few sources of live- lihood to a large proportion of the poor of Funchal^ numerous insects of subcortical and lichen-infesting tendencies are subject to be naturalized (provided they can adapt themselves to the change) in altitudes lower than their normal ones : so that there are many chances, even a priori^ in favour of the T. Lowei having over- spread^ whether by natural or artificial means^ a wider area than its congeners. I believe that there is no such thing as a Tarphius in the Canarian Group : neverthe- lesS;, singularly enough_, a representative, which is more akin to the T. Lowei than to any other hitherto dis- covered (and which was imagined until lately to have been the sole exponent of the genus), namely, the T. gibbulus^ Germ., occurs in Sicily. From which data we arrive at this significant fact : that, whilst Madeira proper is, without doubt, the original centre of the Tarphiiy two species (one of which is, likev/ise. Ma- deiran) are found in Porto Santo, to the north-east of it ; whilst a third makes its appearance in an island of the r Mediterranean. The genus Acalles presents a nucleus of species in the Canaries, moulded on a very large pattern. A closely g3 ■1^ I' \\m l!t \ m m mfkt / m^ 4 1 ■' 1*1 I / 134 %i r- y ^*-N \ \ allied member^ the A. NeptunuSy Woll. (which may per- haps be in reality but an insular modification of the A. argillosuSy Schon.^, from Teneriffe) _, has been detected on the rocks of the Salvages^ to the north of them; whilst on the Dezerta Grande^ one of the most southern stations of the Madeiran Group^ we have a third^ which displays far more in common with the Canarian type than it does with that which obtains in Madeira proper ; w^hich last is gradually^ in its turn^ merged into the ordinary European form. ^ The genus PederopuSy WolL^ is another instance in point. I possess three or four species ffom the Grand Canary^ Fuertaventura^ and Teneriffe ; and I believe it will be found^ on inquiry, to attain its maximum in that cluster. Unlike the others, however, which we have just cited, it is powerfully winged ; and we should consequently expect to trace the evidences of its northward progression with comparative perspicuity. Can we therefore do so ? Yes : in Ma- deira proper it has two representatives, and in Porto Santo (to the north of it) one. And so -wiih. Xenostron- gyluSy Woll. (which is likewise winged), we have two species, at least, in the Canaries ; one in the Madeiras ; and a third, unless I am mistaken, in Sicily. The genus Ditylus is shadowed forth in the Canary Islands by two or three singular representatives of a pallid, testaceous hue ; and, although the group is entirely absent in Ma- deira, a species (the D. fulvus^ Woll.) is found on the w ^ Great Piton ^ of the Salvages, so nearly resembling, except in its smaller size^ one of those from tlie Canaries I / : L 125 tliink insular state of that insect. Deucalion^ also_, may be quoted in support of this twofold hypothesis^ of the direction^ and the slowness^ of the former migratory movements. It is an apterous genus^ and of eminently sluggish habits ; and what is the consequence ? — we have a very remarkable species (the D. oceanicumy WoU.) on one of the rocks of the Salvages^ whilst another (the Z). Desertarum. WolL^ has been isolated on the two /- Madeiran nature is this last, that, although physically ] unimpeded, it has not, even to this day, overrun the surroundin was submerged, it was originally saved from destruction. L } imnressed unon me when I first detected it, that I shall perhaps be excused .pitulat themselves to my cc There is no Madeiran more Confined appa- rently, so far as these islands are concerned, to the remote and almost inaccessible ridges of the two south- ern Dezertas, it would seem to bid defiance to the most enthusiastic adventurer who would scale those dangerous heights. Its excessiverarity, moreover, even when the localities are attained, must ever impart to it a peculiar value in the eyes of a naturalist ; whilst its anomalous structure and sedentary"^ mode of life give it an addi- * " When we consider indeed the apterous nature of Deucalion, m-m iiM 4 1 ^ wi / / M- K F |J - ■ B -1. ] i h 126 f V-.-^ tional interest in connexion with that ancient continent^ of which these ocean ruins^ on which for so many ages it has been cut off, are the undoubted witnesses. Approxi- mating in affinity to Parmena and Dorcadion^ yet pre- senting a modification essentially its own^ it becomes doubly important in a geographical point of view ; and it was therefore with the greater pleasure that I lately received a second representative^ from the distant rocks of the Salvages^ — midway between Madeira and the Canaries. Differing widely in specific minutise^ yet agreeing to an identity in everything generic^ they offer conjointly the strongest presumptive evidence to the quondam existence of many subsidiary links (long since lost^ and radiating in all probability from some interme- diate type) dming the period when the whole of these islands were portions^ and perhaps very elevated ones, of a vast continuous land. ^ ?ic ^ ?ic ^ The Deucalion Desert arum is of the utmost rarity_, the only two*^ speci- its subconnate elytra^ and its attachment (at any rate in the larva state) to the interior of the stems of particular, local plants, or its retiring propensities within the crevices of rocks ; we are at once struck with the conviction, that, during the enormous interval of time which has elapsed since the mighty con yuls ionswhich rent asunder these regions terminated, it has probably never removed inany yards from the weather-beaten ledges which it now inhabits/^ * Since the above was published, I have succeeded in detecting one more example, — namely (in June 1855) on the summit of the Ilheo Bugio, or Southern Dezerta, within a few yards of the self- same spot where it w^as found by the Rev. R. T. Lowe in May 1850. Although I searched diligently on the Dezerta Grande, during my late campaign in the Madeira Islands, I w^as not able (so great is its rarity) to discover farther traces of it on that rock. f >^ I 127 mens which I have seen having been captm I 'I Lowe, in 1850) on the respective summits of the Middle and Southern Dezertas. So local indeed does it seem to be, that it, apparently, has not extended itself even over the Dezerta Grande (where there are no external ob- stacles to bar its progress) ; but retains the very position which in aU probability constituted its original centre of dissemination at the remote period of time when this ancient continent received its allotted forms . Judging from the slowness Anth which creatures of such habits must unlikely that the present one could circulated im that the Southern Dezerta, with the adjacent part (then embraced whole area of its actual primseval range,— the remains of which (though they be now separated by a channel) it stiU continues to occupy, and from which, even when unimpeded, it has never roamed* ;; my province in this volume to draw from cal, I shall perhaps be pardoned for adding a few words on the testimony which the Land MoUusca of the Madeiras would seem to afford, in support of the general mi continent d * Insecta Maderensia, p. 435. 4*1 ir* '] k ipi> ■!■ \\-'% ^^ )\¥tl m 138 of myself, on every rock and island of the group^ Lave^ it appears^ so nearly exhausted the whole number of species which lately remained to be fonnd^ that the con- chological statistics are perhaps^ at the present time^ more accurate than those of any other department of the fauna : and^ independently of the modifications which have been manifestly brought about^in some few instances^ by isolation^ since the periods of subsidence^ it is truly singular to remark how every detached portion of the ^ entire cluster harbours real species^ which are now pecu- liarly its own. Thus (to select an illustration from amongst the most anomalous of the endemic forms) ^ we have in Madeira proper^ Porto Santo^ and on the South- ern Dezerta^ respectively^ true representatives^ in the Helios tiarellay coronata, and coronula^ — which in all probability still occupy the positions (or nearly so) of their original debut upon this earth. Considering the sluggish^ or sedentary, nature of the Terrestrial MoUusks, it is extremely likely (nay, almost certain) that many intermediate links, radiating from the same type, were lost for ever, when the gigantic movements which rent this ancient region were in course of operation : so that, if such were in reality the case, we need not be surprised that one at least of this small geographical nucleus should have been preserved on three of the existing islands of the group. That these are actual species (saved alive from their fellows, after the wholesale destructions in ^ this Atlantic province had been completed), and no results of insular development, is demonstrated by the ii I ! \l Madeira, and the H. H. latens Santo; the H. Madeira, and the H. depauperata in 16 H. Dehhimla in Madeira, and the H. tectifc g5 129 fact that two of them (for the third has apparentlj^ become extinct) have not altered one iota since the fossil /^ period, which, in the opinion of Sir Charles Lyell, is anterior to the dissolution of the intermediate land ; whereas, had they been mere modifications of each other, induced by the local conditions and influences to which they have been, through a long series of ages, severally exposed, the difference between their recent contour and that of their fossil homologues would have been doubtless at once conspicuous. I gather, therefore, that like the Tarphii, to which we have lately drawn attention, they are veritable surviving members of an esoteric assemblage which found its birth-place on this post-miocene (?) tract. In a similar manner, the H. undata in Madeira pi per, the H. Vulcania on the Dezertas, and the H. Por\ sanctana in Porto Santo, are representative species, each occupying the same position, and being equally abundant, on their respective islands : and, although it may be a problem whether the second of these is not an insular modification of the first (or vice versa) ; yet, with the analogy of the three already mentioned before us, I am inclined a priori to view it as distinct. These, also, occur in a subfossil state ; and no alteration appears to havTbeen brought ^out, by either circumstances or time. And so it is with numerous others (as ii 14 \- I'- ^ \ [ ^i t ^'if'-r\ $^\ ^ 4 9 V J^- ^' \ \ \ ^ l^'>' i»tfl '^'- 130 M; J sentative inter se. Prom wliicli we are driven to con- elude; — ^first^ tliat this quondam continent was densely stocked at the beginning with foci of radiation created expressly for itself^ ; and^ secondly^ that the areas which these various creatures had overspread^ before the land of passage was broken up^ was extremely limited^ — or^ which amounts to the same things that their migratory progress was unusually slow. Touching the two-fold question^ of the local engage- ment of this Atlantic district with specific centres of diffusion, and the eoctt lowne0 of^eir diffusive pro- gress^ much instruction may be derived from a contem- plation of the conchological statistics. Porto Santo, for instance, is a very small island (not more than seven miles in length), yet the number of endemic species which it includes is so perfectly astounding that it may be appropriately termed a generic area of radiation. * It would seem, when viewed on a broad scale, as if particular districts throughout the world had been made as it were the special fields for the exercise of the creative force, — or that, generic areas yf Thus, Professor E. Forbes records his belief that most, if not indeed all, of the ter- restrial animals and plants now inhabiting Britain are members of specific centres beyond its bounds, — they having migrated to it over a continuous land, before, during, or after the glacial epoch. Hence, since the greater number of them are supposed to have come from the central Germanic plains, w^e may assume that those plains were one of the primary areas of diffusion for a large mass of created beings. There is good cause for suspecting that the Pyrenean region may have been another ] and certainly all evidence would tend to prove that this vast Atlantic province was, also, well stocked with aboriginal forms. 131 Nor does tHs primseval excess of its aborigmal more maj them since the remote era of their birth. Although a few have apparently died ouf^ since that epoch, conse- quent perhaps on the change of level and diminished range which took place during the process of subsidence ; ^ 4 4^ d/K -\ h* \ we are amazed to find that certam species wnicn are now limited to particular spots (even whilst unopposed by physical barriers) have been absolutely peculiar to them * Assuming the Helix Lowei and Bowdichiana to be gigantic phases of the H. Portosanctana and punctulata, respectively ; four only, namely H.fluci^osa and lapicida, Achatina Euhna, and Cyco- M^^lucidum (the first three of which are extinct throughout the entire group), seem to have altogether disappeared. Nevertheless, the gradual dying-out, as it were, of species, ^o^ here and m Madeira proper, is singularly evident. Thus, m tlie latter the Cam- cal beds show the H. tiarella to have been once most abundant (it literally teems in those calcareous formations). Yet so rare is it m a recent state, that, until the summer of 1855, when it was detected by myself and the Rev. R. T. Lowe in two remote spots along the perpendicular cliffs of the northern coast, it was supposed to have been lost for ages. And the same may be said of its counterpart, the H. coronata, in Porto Santo,-which, likewise, swarms in every fossil-bed of that island; but which was, also, until I met with it. on the 15th of December 1848, adhering to slabs of stone at a con- siderable depth beneath the ground, on the extreme eastern peak (opposite to the Ilheo de Cima), imagined to have long passed away. And so, reasoning from analogy, I think it far from impro- bable that the third representative of this little geographical assem- blage,-the H. coronula of the Bugio (which has hitherto only occurred in the mud deposits on the summit of that rock),-may be still alive, though perhaps in very small numbers, on some of the . inaccessible ridges of those dangerous heights. -^ t U^ ^ \^ >iM 141^' Lu^ 3 ■h ■-.-■^^ ! I- i v \ 132 from the first^ — or^ in otlier words^ that^ whilst the fossil deposits extend throughout the lower regions of the island^ far and wide^ it is only in those respective por- tions of the beds which join on to the present ^^^ habitats ^^ that the fossil homologues of several of the species are met with H. Wollastoni in point. Madeiran Mol m of the Pico de Conseilho^ of Porto Santo^ April 22^ 1849 ; and the subsequent explorations of the Eev. R. T. Lowe^ my own proved that it occurs else except upon that single slope. Throughout the large expanse of calcare- ous incrustations which are spread over the island else- where^ and on the adjoining Ilheo de Baixo^ all of which teem with shells^ I think I may assert^ without fear of contradiction^ that the H. Wollastoni does not so much as exist. Yet at the Zimbral d^Areia^ which the Pico de Conseilho directly overhangs, — a rich tract for these fossil remains, — as well as in the muddy composition of r a cliff near at hand, it literally abounds. In like manner, we might recall many others which peculiar, recent and fossil H. which swarm on the summit of the Ilheo de Baixo, in both states. H, attritay again on of the H. r)G only in the beds towards the base of that mountain that its fossil homologue is found. But what do these facts 1 f\ I ^— — ■ pv .., ^ r"— 4.^- 133 indicate? Surely they tell us p already so often insisted upon^ dancy of this once continuous land with specific foci of ■nam the redun- sedentary primaeval ra( We must endemic Helices mor lities for diffusion than the rest, and paupercula seem not only H, \ Madeiras ments, but to have even found their way to tnat uistanx portion of it wHch now constitutes the Azores. The H. pohjmorpha has also penetrated the Madeiran region throughout ; and being, like the H. eruhescens, peculiarly sensitive to the action of external influences, we per- ceive, in consequence, that almost every island and rock has now its own especial phasis of it. So greatly indeed is that species beneath the control of local circum- stances that the very districts of an island as insignifi- cant as Porto Santo have each their separate races to boast of. On the Pico d^Anna Terreira it assumes a form to which the name of H. attrita has been applied ; \ H. and, in Zimbra d'Areia, on the Pico de Conseilho, an Ribeira da Coxinha, it is the H. pulvinata; many other situations widely removed inter se, it puts on the shape (variable, both in size and hue) to which +l^r. iitlp, of B. discina has been given. But, if we leave J I m. m mi if \m I ' . I \ ■-■ ^ri-i- ^J-|^ .MM £ -^>J ± ^-» 1 J ■^■3 < I J 4 134 ^J ..\ "> ^ -^ ^ \ \ ^ m I Porto Santo^ and follow this Protean Heli^ into the other divisions of the group ; we meet with it on the Dezertas as K from the much more open umbilicus is the case in the northern and southern ones)^ whilst in Madeira proper it constitutes the H. lincta (with an additional pale variety for the calcareous district of and the H. saccharata^ from the Sao Lou- renyo promontory. In the same may we might pursue the H. erubescens^ and show that in the sylvan regions_, and on the low barren Ponta Sao Lourenjo of Madeira^ on the Pico de Facho of Porto Santo^ on the Ilheo Chao^ on the Central Dezerta^ and on the Bugio (where it at- tains a gigantic size)^ it has its distinct and permanent phases, — the evident results of isolation, and other topo- graphical influences, since the subsidence of the inter- vening tracts. And in like manner, the Clausilia clelto- stoma is universal throughout the Madeiran Archipelago, — displaying, however, in Porto Santo a fixed and strongly ribbed state, peculiar to that island. Thus, if the examples which we previously cited tend to establish the extreme slowness of the migratory movements of the terrestrial mollusca across this former continent, the present ones (which refer to a few exceptional species of quicker self-diffusive powers) will show, no less than the insects to which I have lately called attention, that where sufficient areas had been overspread (before the periods of subsidence) for the creatures to have &/^ if f Y 1^ "» \ / JiA-U 1 ^ # >■ uA-w ' 1$ f r // .-^ i f i i 3 / jjj'i^ I f / f M 4 u h :i:\ J rx / ^. ^■" / . ^Tfc: J> ^ ?\ «^. iluM^ ■^j ., 1 f t^ # .^» 1* ^- 135 reached what now constitute the various islands of the cluster, we at once detect traces of this fact, through «4»: their more or less altered aspects, — the result of isola- tion, and diminished range, during the enormous m- terval which has elapsed since the successive convulsions r which caused the partial destruction of this Atlantic province were brought to a close. To return, however, to the insects, after this long con- .^f^UCy chological digression, — I neef 4«k mu my Enough has been said to "^^^^^ render intelligible the idea which I wished to convey. concernina: the aeneral direction of the migratory *> V jitr^ >/ y-m progress,— the former of which I consider probable from the north-easterly course in which creatm-es generi- lii II ^W: U } off; }} were, if we may so express it, " given- whilst the circumstance of their being for the ifi. i i| j*!i' seem the the islands harbour are endemic) would i latter. We must not however forget, that it is only to the aborigines of this quondam land that the above specula- tions apply. Assuming the region not to have been insnlar, that is to say, to have been connected, on its outer limits, with a European, or Mediterranean, conti- nent ; it would necessarily follow, that a certain number of colonists must have found their way over its area, and moreover in an opposite direction to the living !| '^! iiii :^'4 iJlWt ! i«i>) 136 stream (if we may so call it) wliich had been long flow- ing in a north-easterly course across its surface. What- ever be the length of the periods, however, during which these counter migrations were going on, I think it sufficient to state that I would refer them to epochs altogether different,— so that, accompanied as they may have been by special geological phsenomena, which, if known, would in all probability become at once explana- tory, we should be the less inclined to regard as absurd what might appear at first sight difficult to understand. In the case of the British Isles indeed, no less than five of these distinct migratory eras have been assumed, and specified^, by Professor Edward Forbes; therefore (what- interestin necessary at least two in behalf of this ancient Atlantic province. Not are of a less evident, or more questionable, character, he has at any rate proved, I think, almost to a demon- stration, the westward progress of the great mass of our British animals and plants, over a then unbroken land from accurate of Germanic plains; whilst the the late Mr. Thompson of Belfast, concerning the reptile statistics of Ireland, England, and Belgium, respectively, have succeeded in showing, with much presumptive rea- son, how the formation of St. George's Channel, before * Origin of the Fauna and Flora of the British Isles (in Mem. of the Geol. Survey of Great Britain^ vol. i. p. 336, a. d. 1846). h \ \ Wi J-l m 1 137 that of the German Ocean, interrnpted the march of these wanderers to the far West, and debarred an im- mense proportion of them from an entry into Ireland, which would otherwise have colonized that country equally with our own. As regards Professor Forbes' s views of the creation of a vast continent (reaching far into the Atlantic ^') at the close of the miocene epocTi, through the upheaved bed of a shallow miocene sea^ — a region moreover of such an extent as to have connected the various island groups between the Fucus bank and the shores of the Old World, not only with each other, but with a Mediterra- nean province, Asturias, and even the south-west of Ireland,— I must be content to pass them by, hazarding only a few crude and desultory remarks. So large a question, indeed, cannot be safely handled without a corresponding amount of data, in all departments of natural science, to reason from, — which I do not possess : still, if a speculation from entomological premises, per se, be not altogether worthless, I would point to the conclusions (lately adverted to) which my Madeiran researches have forced upon me, concerning the direc- tion of the former insect migrations, — inferences which are, from first to last, of necessity erroneous, if the requisite medium for transit (into South-European lati- * ^^ My own belief/' says Professor Forbes, ''is, that the great belt of gulf-weed, ranging between the 15tb and 45th degrees of north latitude, and constant in its place, marks the position of the coast-Une of that ancient land/' ■, /U' /. -^- ■■^m\ 4 J ^ A^^^ S A' V '■-■ .^ - K t ' ■m: / 1-- - ■' i m 4 J Wh I ff» lit tudes, at all events) be a mere conjecture or romance. Such a notion, however, I would not for a moment entertain, — for there is too much direct evidence in support of distinct epochs of dijEFusion, to allow of any hypothesis, when eiideavo'uring to account for the phsenomena which we now behold, to supersede the continuous No matter we be compelled to suppose, whilst attempting to in- current flowed in exactly opposite courses, at diflPerent and remote fact itself remams here. I am which I had independently arrived, from the insect statistics, does positively require a northerly prolonga- tion of that area beyond the line of the central Mediter- ranean districts ; yet, after making every possible allow- ance for accidental introductions since the subsidences have taken place, there is still left a large residuum which I am convinced can never be explained (unless the doctrine of specific centres be a myth) except through the means of ordinary and regular migration over an unbroken continent. Nevertheless, though I would not presume, from insufficient material, to insist upon an extension of this Atlantic region into higher latitudes than those which I have just referred to I must express my individual belief that, the more the subiect is examined, with reference to tbp rlis+riTin+i"r,n r^f \ 49M 139 Annulosa from In the ^ Insecta Maderensia/ I have idy thrown immediate me either to withdraw or modify reverse") . I will select the following. 4fll £C :tracted from my preface to that work. Taking a cursory view of the Coleoptera here f may described^ the having a greater affinity with that of Sicily than of any other country which has been hitherto properfy investi- gated. Apart from y ]lyi L<-' more of the entire Mediterranean evinced in some of the most c as Apotomus, Xenostrongylm less -^ is especially u.'^ such Tarphius^ Cholovocera^ ju^ ^ mor HoloparamecuSy Berg morphus. There is^ appear to be, some slight (though decided) collective assimilation with what we observe in the south-western own country and of Ireland,— nearly i \ > ii iyi our common to Madeira in those particular i ' point i fully ■] Mesites. Whether or i be employed to further the quondam approximation, by means of a contmuous land, of the Kerry and GaUician hills, and of a huge —■^^ V «.^-i-- »-l-H 'f J J 140 miocene continent extending beyond the Azores^ and including all these Atlantic clusters within its embrace, I will not venture to suggest : nevertheless, it is impos- sible to deny that, so far as the Madeiras betoken, would hensive idea. Mediterranean fauna, the northern tendency of which is in the evident direction of the south-western portions of England and Ireland, and with a profusion of endemic modifications of its own (bearing witness to the engorgement of this ancient tract with centres of radiation created expressly for itself), whilst geology proclaims the fact that subsi- dences on a stupendous scale have taken place, by which means the ocean^s groups were constituted; we seem to trace out on every side records of the past, and to catch the glimpses, as it were, of a veritable Atlantis from beneath the waves of time ^/^ * Although, for want of a hetter name, it may be admissible, when speaking either figuratively or poetically, to allude to this former region (as I have done in the above quotation) under the title of ''Atlantis;'^ yet it seems incredible that certain writers (assuming its quondam existence) should have recently referred to it seriously as the possible "Atlantis of the ancients ! " Consider- ing that there is good reason to beUeve that all these islands were islands in a miocene sea, and that, if (through a general elevation) they were subsequently connected, the land of passage was broken up long anterior to the appearance of man upon the earth, " the ancients" must have assuredly merited their appellation, if they could have thrown any hght on a problem which belongs to an epoch thus remote. Whether the ''Atlantis " had any being at all except in the imagination of the Latin poets, or whether (as Lord '^^tf r 141 The Mesites Maderensis, WolL, to which I alluded in the above quotation, is undoubtedly a strong case m point. Although specifically dissimilar from the M. coun mistaken facie, for that insect Nature which are not merely representative of (or analogous to) each other, but which are actual homologues, or allies, should usually emanate at first from foci not far removed inter se ; or, at all events, if distant, connected by an intervening land :— in other words, that ffenencjireas, form item We system_Ql.C£eated^things w^ ^ detect traces of this primary law in each division, or class, of the organic world ; nor is its reahty as a law interfered with, through the occasional exceptions which selves. ent them- accounted natural or artificial means m m !l «P IT* i ti World now be known ; yet the fact that the InsulcB Fortunata of Juba are almost universally identified with the present Canarian Group (as indeed the accurate description of Pliny well nigh demonstrates), and the Purpurarice with the Madeiras, ought at onfce, apart from geological evidence, to point out the absurdity of the hypothesis, that -In Atlantic continent, in the very position which those islands occupy, could have been acknowledged to have any existence by the literature of either Rome or Greece, W ^' ^ (A y V ■h * i \^ V x.X^ e- I 4. . ^. Ik { { i' c •- \ \¥t 143 •M . : r affect the subject^ as a whole. Sometimes indeed they become at once intelligible from the historical records connected with them_, proving that hnman agencies have been at work acting as transporting media^ within a period comparatively recent ; whilst at others^ the fact of the creatnre having been endowed with self-diffnsive powers to an extravagant degree may sncceed equally in rendering the phsenomena explicable. But^ even where neither of these solutions would seem to suffice^ we should still recollect that it is only in the mass that such questions can be pronounced upon; and that^ con- sequently^ where we are able to discover a rule which is for the most part adhered to^ it is more philosophical to conclude that the departures from it are the result of special disturbing causes (whatsoever they may have been)^ than to permit them to undermine our faith in what would be otherwise universally true. Thus, the botanist teUs us of Ixias, Stapelias, Mesembrianthe- ^ mums, Pelargoniums^ and Euphorbias, as concentrated in Southern Africa; of Magnolias in Central America; of Calceolarias on the Andes; of Myrtles, Banksias, Mimosas, and Eucalypti^ in Australia; and of the Bread-fruit Trees in the South Sea Islands : the orni- r" thologist points, inter alia, to the Toucons and Hum- ming-Birds from South America and the West Indies ; whilst the student of the higher animals informs us of the Kangaroos (indeed of the whole of the subclass Marsupialia^ except the genus Didelphys) as peculiar to Australia and a few islands to the north of it ; of Lemur y 143 Mada Porcupines, and of Alligators, and of the Platyrrhini (amongst the Monkeys), to South America; and of the Ourangs to the islands of the Indian Archipelago. And so it is with the Insect a; many of the larger groups of which (as Amycterus and Paropsis^ in Australia; Pachyrhynchus and Apocyrtus^ in the Philippine Islands ; Hipporhi MonocheluSy Dichelus^ and Moluris, in ca : Macronota, in Java ; and Naupactus, Hypsonotus, Centrinus, Platyomus, and Cyrtonota, in South America) are confined to countries of propor- nitude, whilst the smaller mon gions, according as local circumstances may require pri- mary adaptations to harmonize with them. Thus, whilst we frequently find an extensive genus diffused over the greater portion of the known world, we perceive that even its structural characteristics are not uniform throughout, but modifications imen — ^which have often, turn been described as such. Whether genera, however, or not, they are undeniably small topographical assemblages, satellites around their central types; and they may therefore be safely regarded as genera, if we choose to view them in that light. Of such a nature I have already pointed out* is Saprinus, as compared with Hister ; Atlantis with Laparocerus ; and Oxyomus with — * Insecta Maderensia, p. 214. ik -P !' tW !i:|lt ! m i » mm ' I . >4j Hii»» r i Ml t i J^ A .H> ^ M^ •m 144 AphodiuSy and^ I might also add^ Mesites with Cos- sonus. I believe indeed that Mesites will be found to attain its maximum on the Pyrenees (I already possess two or three species^ in abundance^ from that region) ; and^ if such should be the case^ we shall be able to ap- preciate the significance of two representatives so closely allied as the M. Tardii and Maderensis^ — one of which has been given off in the direction of Ireland^ and the other of the Madeiran Archipelago. But I will not digress further on the subject of this Atlantic province; since^ however much I may indivi- dually regard it as a reality of the past (which the Coleopterous statistics have compelled me to do)^ it must of necessity remain^ as heretofore^ a matter of much controversy and doubt. I should indeed apologize for having trespassed on the reader^s attention^ in wandering ^ thus far from the immediate results of subsidences^ — which I proposed^ at the outset of this chapter^ to exa- mine^ with reference to the impeded diffusion of the Annulose races. Nevertheless^ concluding that a prac- tical illustration of the effects of one of those great downward movements to which geology so repeatedly bears witness would not be irrelevant to the assumed consequences which I had previously ventured to define^ finished wi V considerations which should not be omitted^ when inquiring into insect distribution as influenced by geolo- gical pheenomena. m\ 145 i»' Next and sinkings (traces of one or the other of which are more or less manifest in almost every region of the world), natural barriers may be cited, — as presenting, not un- frequently, insurmonntable obstacles to the self-dissemi- nation of the insect tribes. By natural barriers, how- ever, I would be understood to imply natural primary barriers, — or, in other words, such as have continued as barriers ever since the present animals and plants came into existence upon the earth. For, the ocean (by way of illustration) is a natural barrier ; and yet it is not necessarily a primary one, as may be readily gathered from the above remarks, in which the results of subsi- dences are discussed,— subsidences which have had the effect of letting it in over portions of an already tenanted, and unbroken, continent. Mountain-chains, also, are barriers ; but it may happen that they have not been so from the beginning, — as in instances, for example, where they have been gradually upraised during periods geolo- gically recent. But both sea and alpine ranges are barriers, when (as usually happens) they have remained as such since the creation of the several species which our Mr this distinction, whilst commenting upon the marked divergence of the faunas on the eastern and western IS m slopes of the Cordillera. " This fact,'' says he, ' perfect accordance with the geological history of the have existed as a great Andes ; mountains smce H I Irif 1 M f llftil li ^3TTl f _ i 146 and therefore^ unless we suppose tlie same species to have been created in two different places^ we ought not to expect any closer similarity between the organic beings on the opposite sides of the Andes^ than on the opposite shores of the ocean. In both cases^ we must leave out of the question those kinds which have been al^le to cross the barrier^ — -whether of solid rock or salt- water*^"/^ Conceding^ therefore^ this distinction between barriers of a primaeval and more recent character^ it is not diffi- cult to understand why the opposite sides of an alpine chain^ as well as countries separated by the sea^ should display different phsenomena from each other. On the contrary indeed^ if we could feel satisfied that no means of accidental transportation had operated to take them there^ and that the animals themselves were incapable of enduring great diversities of temperature^ and other con- tingencies ; we should be startled to di-scover creatures specifically identical in such regions^ — so long at least as the doctrine of unique centres of radiation formed part of our zoological creed. We must not^ however^ be too hasty in questioning (if I may be pardoned for the com- pletion of a metaphor of which I thoroughly disapprove) this article of our faith^ through the occurrence of simi- lar beings in areas between which there exist barriers^ both primary and well-defined; for the methods of diffasion are so complicated and numerous^ that^ even where human agency (that most important of elements) * Journal of Researches, pp. 326. 327. -1 j: ^ ^^ mn. 147 is not concerned, what at first sight may frequently annear to be impossible becomes clear enough when more critically inquired into . S ome species, we know, are gifted with greater powers for horizontal and vertical progression than their comrades, and can (though they rule) extremes of atmosphere sufficient to render even lofty mountain Others, as the Calosoma Syncophanta of Europe, have been stated to ^ traverse the ocean unhurt* ; and I beheve that many do ^ at times accidentaUy arrive, in a half^drowned state, especially after boisterous weather, across channels of y" considerable breadth. Mr marine rejedamentay durin on examining tlie currences writes as follows ; cc w from ing into the water, had been brought back by the tide ; or whether they had succeeded in the attempt to pass \ ( from the continent to us, by flymg as lar as tney coum, * Many of the Cahsomata would appear to possess this power of crossing, either by flight or by abandoning themselves to the waves (though more probably by the assistance of both), even ma- rine barriers with impunity. Numerous instances are on record to this effect ; and I am informed by Mr. Darwin that a Calosoma flew on board the ' Beagle,' off the Bay of San Bias, in South America, whilst they were ten miles from shore. It seems likely, therefore, that the occasional occurrence of the C. Syncophanta in our own country along the southern and eastern coasts, is due to this generic capability,- and consequently (as indeed it is usually acknowledged to be), the result of accident. h2 r s. * J ' I H :j N. I liKf M ■ m4 mi m- 1 148 and then falling had been brought by the waves^ cannot certainly be ascertained; but Kalm^s observation in- clines me to the latter opinion"^/^ And Sir Charles Lyell remarks : — ^^ Exotic beetles are sometimes thrown on our sh^re^ which revive after being drenched in salt w^aterf." Nor should we forget that chance agencies of every description^ which we are too apt to overlook^ are daily at work (and have been so since^ at any rate^ the last creative epoch) to transport these variously organized beings beyond their original spheres. Sometimes they are carried on^ or within^ the bodies of larger animals^ which is especially the case with the parasitic tribes ; at others on floating trunks of trees^ and casual substances of divers kindsj which are able to resist for a definite period the destructive action of an element saturated with salt. Unwilling victims^ again^ are ever and anon hurried to comparatively distant lands by the very winds that blow ; and not only to distant lands^ but over altitudes in which the severity of the cold w'ould quickly annihilate them^ were they (as perhaps usually _ p happens) to be deposited there on their headlong and compulsory com^se. ^^ As almost all insects are winged J/^ says Sir Charles Lyell,, ^^ they can readily spread them- selves wherever their progress is not opposed by un- * Introduction to Entomology, ii. p. 13. t Principles of Geology, 9th ed. p. 657. X Although this is true on a broad scale, a reference to my ob- servations in a preceding chapter will show, that in some countries, especially islands, the reverse will frequently Be found to obtain. /' 149 congenial climates, or by seas, mountains, and other physical impediments ; and these barriers they can some- times surmount by abandoning themselves to violent gales, which may in a few hours carry them to very con- siderable distances. On the Andes some Humboldt 19 180 feet above the sea, and which appeared to him to have been involuntarily carried into those regions by ascending currents of wc*.'' With numer is not to the winds alone that we must look for an ex- planation. Large and rapid rivers are liable to inun- date their banks and bring down insects in prodigious which are disgorged into the ocean, and car- masses. ried to a distance from the coast, in proportion to the violence of the ejecting stream. When the body of water is considerable, the sea becomes diluted to an un- creatures om may be deposited, by means currents into which they are borne, on neighbouring islands and continents. Even the Hydradephaga are thus occasionally transported; for Darwin mentions having captured a Colymbetes off Cape S*^ Maria (to the north of the Kio de la Plata), when forty-five miles from Journal he records the following remarkable facts, which bear immediate '^ On another occasion * Principles of Geology, p. 656. « Ijr ilr i^ il iil.|« iii ^ I I tiiy 1. I ' I 1 ^ ■ ^ ' E WIMt ■ff' LT^. A ^ \ bV t t '!„ ^-_- I m Mf f} «# mk til I 150 when seventeen miles of£ Cape CorrienteS; I had a net overboard to catch pelagic animals. Upon drawing it up/ to my surprise I found a considerable number of beetles in it^ and, although in the open sea^ they did not appear much injured by the salt water. I lost some of the specimens ; but those which I preserved belonged to the genera ColymbeteSy HydroporuSy Hydrobius, Nota- phus^ CynucuSj Adimoniaj and Scarabmus. At first I thought that these insects had been blown from the shore ; but upon reflecting that_, out of the eight species, four were aquatic (and two partly so) in their habits, it appeared to me most probable that they were floated into the sea by a small stream which drains a lake near Cape Corrientes. On any supposition, it is an inter- esting circumstance to find live insects swimming in the open ocean seventeen miles from the nearest point of land^/^ Accidental means of dissemination, such as those to which I have just alluded, and others to which we might appeal, will generally account, and with much presump- tive truth, for the many exceptional cases which present themselves, during our investigation into the effects of natural barriers, as visible in the distribution of the Annulose races, on the earth^s surface. I say ^^ excep- tional cases,^^ because any one who has laboured practi- cally in mountain tracts cannot have failed to recog- nize the marked difference which is often displayed by the insect population on opposite sides of some alpine * Journal of Researches, p. 159. K \i rfi i 151 chain ; whilst he whose lot has been cast amidst island will have become pediments have been placed (in this instance by the broad arms of the mighty ocean) as checks upon a too rapid system of diffusion. mountain amon most cient age in sitUy are Nature's barriers against the self- dispersion of the animate tribes ; it follows that, if the two could be (as it were) united, we should have found the greatest ob- stacle which physical conditions can ordinarily present against the wandering capabilities of the latter. The question therefore arises^ so joined ? Undoubtedly it is : and hence we arrive at them should >/ have overspread, which any country is able to furnish. Madeira is a mountain island, — its highest peaks rising, although resting on so small a base, to an alti- tude of more than 6000 feet. Yet it is only partially a case in point; for, although it was a mountain mass, and perhaps a very elevated one, when its endemic beings made their first appearance upon its surface, we have already intimated that it has become isolated since that epoch : so that, whilst one of the natural barriers niountam may the sea, as it now obtains) has played, as an agent of m- m s I ! I BIK. n m^ \ 'm 3 fi Ml I IP fr y V - — T-rT\s - i_- - j_ LJX~ -L T -_ JIj- -trt-^^^Tr" ^tfl »» l«t^> ^^ 'li 'It 152 obstruction, but a secondary part. Still, there is good reason to believe that the ancient tract of which it is a portion was broken up at a comparatively early date after the creation of those peculiar organic forms which found their birthplace within its bounds ; and that, con- sequently, the latter could not have wandered far (if we except those species on which unusual powers of diffu- sion were bestowed) when the land of passage began to give way particular stance^ partakes almost of the character (no less tha^ mountain Madeira nature and where^ consequently^ we may anticipate those ultra phsenomena of areal limitation upon which we have been just commenting. But let us now inquire^ whether the hypothesis at which we have arrived will stand the test of experience ; for unless it will do so^ we might have been spared the labour of propounding it. Madeira is a country com- r posed of narrow mountain ridges^ which radiate from central crests^ and form the lateral boundaries of deep and precipitous ravines. Modifications of this structural type are of course traceable everywhere; the upland tracts are often undulating and broad^ and the buttresses which slope towards the sea are sometimes expansive r and irregular : yet upon the whole the above description is correct^ and we may accept it in a generic sense. Now we may premise that_, even to this day^ it is an / m 153 more island of floods; therefore, tow much have been so when its primseval forests, in all their splendom^ caused an amount of exhalation and moisture of which at present we can have but a remote conception ! Hen may most fusion would not have taken place, in the course of ages. modern fauna, m a large measure homo Yet, in spite of this esoteric surprism districts r Scarcely a gorge or woodland serra exists within its harbour its own!' and in many instances the ranges of these creatures are so local or confined, that they might be easily overlooked even in their respective neighbour- hoods. It is certain, however, that the floods (t " ' " Inch happen periodically) have done considerable work in naturalizing many of the subalpine forms, which could adapt themselves to the climatal change, in altitudes below their normal ones: and, in the north of the island, where the temperature is cooler than on the opposite side, and where the lofty defiles terminate, even at their lowest outlets, in abrupt precipices along the coast, so that the rejectamenta during the annual rams are brought into direct contact with the shore, this gradual process of deportation is particularly evident,— a circumstance to which I have already alluded else- H 5 4U^ O^ Oi 1 <vH^ I ^ I y. f -' .' * .^ ^ \ i«4 \ I f t j^ \ i^t. J-f- '\iAJ*' \ l^ \ ai t/- i Wffli * ^. >■ JU fr \ \«>.»5 -'li^lt- fti ■■■ i I 154 where ^. But^ after making due allowance for tliese powerful means of dissemination (wliich_, in tlie common order of tliings_, must necessarily obtain in mountain islands y as it were^ par excellence)^ the fact still remains^ tliat in the Madeiran Gronp the acquired areas^ even up to the present date^ of a vast proportion of the insect inhabitants^ are wonderfully circumscribed. The real state of the case^ however^ would appear to be simply this : that the floods^ although they may have tended to diffuse the members of a comparatively uniform alpine fauna in the various clefts or gorges beneath^ can have ^ had no power to combine the aborigines of the several gorges themselves ; and^ since a large proportion of the ■ * endemic species of those islands are (as I have previously stated) apterous^ the perpendicular edges of the ravines^ which in many instances rise to an elevation of 2000 feet^ have acted (and ever will act) as impassable barriers to vast numbers of the insect tribes. With this single example (by way of illustration) ^ which the Madeiras have supplied^ I will take my leave of the question of natural barriers ^ as tending to regulate the topographical diffusion of the Annulosa^ — feeling that I have already devoted too much time and space to this portion of the subject (if such indeed it be) which I had proposed in the present treatise to discuss. Other barriers might have been adverted to^ — such as large rivers^ extensive deserts^ and thickly set forests (espe- cially of pine-trees^ which frequently offer a very decided r * Insecta Maderensia, p. 81. hi;i 155 impediment to insect progr ess) ,— but they are of secondary importance, when compared with marine and may from just entered into. My main object has been to draw attention to the fact, that the great obstacles which Nature has placed against the too rapid dispersion 1 more matter r r investigations into entomolo than it is, during our 1 geography. To be sur especially in a country where the species are principally wingless, that we do not discover indications of a general uniformity in its fauna, involves an absurdity,— unless mere coinao-e of the brain. But, if we believe in that theory im must consistently with ourselves, and not anticipate phseno mena for them. We ar( tion between the sciences, as though each had its own propositions to establish, and nothing more: indeed, would assume (though perhaps tacitly) , that what is proved to be true in one depart. at least, rendered inconsistent (if not ^1 ^'> may actually negatived) in another. swx r refute,— since a principle wHcli is true, its i '1 ■ I! ^m I : , L \ iiliia ■'{ I m I tfr « ^ Wl iti-t H** If m i' mm' w ^^ 156 is true under every circnmstaiice and condition; for otherwise^ it could be both true and false. We need not therefore be afraid of comparing truth with truthj under whatever shape it may arrive_, as though it were possible that either of its phases could ever suffer from the ordeal of a close contact ; since^ if they be really true^ and free from deception^ they must needs go hand in hand^ and may become (however opposite they be in their subjects) directly explanatory of each other. The astronomer who is not intimately acquainted with pure mathematical analysis^ in its various aspects and bearings^ is in fact no astronomer at all. The geologist who would interpret the grand phaenomena of the eartVs crust apart from statical and dynamical knowledge^ and without the help which the chemist^ mineralogist^ anatomist^ zoologist^ and botanist can afford him^ stands a fair chance of leaving his problems unsolved ; whilst the students of zoology and botany who would endeavour to understand^, and account for^ what they see in the animal and vegetable worlds around them^ without must pared to fail signally in their attempts. indeed must and not only in concert^ but as mutually assisting each »wn for those inferences which arise other. '^By the he. may be discovered; from the application of general truths to the particu] things and cases contained under them^ must be just.*^ * Religion of Nature Delineated, pp. 73, 74. yy - 1 »f I I 15 r 4*i mp \ 1 CHAPTER VI. THE GENERIC THEORY. 1 / 2Teat of the organic world, how perfect in each separate part, how complete and harmonious the whole ! The unity of the comprehensive plan, amidst the infinite modifica- tions which it includes, has ever heen a theme of admi- ration and delight ; for the mind, which has once caught a glimpse, even in physics, of what it is not possible to disprove, instinctively clings to it, as to a grand material truth. The discovery, at all times, of what we feel to be actually certain is in itself so fascinating, that the very more mere our climb from at a slow and even pace, we hail with inward satisfactior may more quickly onwards (gradually though we must of necessity advance) towards its final accomplishment. may msis extravagant dissimilar are everywhere to be met f 1 i il< -. . I I 4^ i m mt It 4» M t «VHtlf i i f i ll!fV tii m^ 1 158 ivitb. ? Is it possible to recognize anything like a unity of tvpe amongst creatures so differently constructed^ and so widely removed from each other in their habits^ aspects^ functions^ and attributes? Such questions as these^ however^ though they may occasionally perplex the tyrOj or amateur^ are not likely to be raised by any- one who has mastered the merest alphabet of zoology^ r and who is aware that the integrity of Nature is some- thing real and positive^ as experience indeed is ever tending more and more to corroborate, and by no means dream iment mark visible in the intermediate grades^ the first rudiments of ore-ans and instincts wliicli are destined to attain tlieir maximum in the liiglier ones^ embody but a small portion of what it is the naturalist^s mission to investi- gate. To him belongs the special pri\dlege of inquiring dogmatically into this structural advancement ; and of suggesting methods of classification which shall accord_, in their several component divisions^ so far at least as is practicable^ with the constitutional change. We should recollect, however, that this system, being based upon truth, must, if it would be consonant throughout, adapt itself to all the various phsenomena (in their respective positions, in the scale), from the consideration of which it should be exclusively deduced, or built. To draw broad conclusions of any kind, or to attempt the esta- blishment of propositions and principles, from simple r jT - 159 dialectics, without a previous training in the practical bearings of tlie subject, would be absurd, and almost certain to beget error. "It cannot be that axioms establisbed by means of reasoning [alone] should be of any value for the discovery of new results ; because the subtilty of Nature far exceeds the subtilty of reasoning. But axioms duly and orderly abstracted from parti- culars, in their turn easily point out and mark off new ' Such particulars; and so render the sciences active"^. were the words of the greatest philosopher which this country has ever produced ; and it would be well, whilst examining the causes of what we see, and endeavouring to obtain some faint and distant notion of the vast scheme of Nature as originally designed, to keep them constantly in view,— lest, by trusting to theory only, observation and facts; or by venturing to pervert the latter (instead of being led by them), so as to tally with our preconceived ideas of what ought to be, we miss our road, and become lost in the mazy labyrinth of our own fanciful inventions. With this preliminary stricture on the express duty which devolves upon the naturalist (with whom the from senomena make and * " NuUo modo fieri potest, ut axiomata per argumentationem constituta ad inventionem novorum operum valeant ; quia subtihtas uaturse subtilitatem argumentandi multis partibus superat. Sed axiomata a particularibus rite et ordine abstracta, nova particularia rursus facile indicant et designant; itaque scientias reddunt ac- L tivas." — Novum Organum, Aphoris. xxiv. s ! 1 ^ tttfi ! (li^ . i ^ f* mi 4' 1 II 1 i itii 160 ir I argument^ tlie basis of his various doctrines^ — at any rate of those in which the critical subject of arrangement is concerned ; I shall perhaps be pardoned^ after haying been drawn^ in the preceding chapters (however involun- tarily)^ into the question of ^species/ as rigidly defined^, if I now offer a few passing remarks on the theory of genera. There can be no doubt that amongst a large class of ordinary observers a clear perception of the generic system^ in an abstract sense^ does not by any means prevail. What the nature of a genus really is^ would appear to have been very commonly overlooked^ or per- haps misunderstood^ by people of this stamp ; and the consequence has been_, that the wildest notions have frequently arisen^ even from men of sound specific attainments^ as to the claims (for annihilation or re- tention_, as ^ genera^) of certain subsidiary zoological assemblages. The terms '^ genus ^ and ^ species^ have been conjointly so long associated in our minds with the selfsame things (whatsoever they may be)^ that they have become almost part and parcel of the objects them- selves; so that the student who does not sufficiently reflect on their true signification^, is apt to regard them as of equal importance^ — or^ rather^ more often perhaps than otherwise^ to make the latter subservient (or inferior) to the former ! This however is^ in reality^ the very reverse of what should be the case^ as a moment^s consideration will indeed at once convince us : for what are genera^ after all^ but dilatations (as it were) along a -I ' ^l ■ 1 :||^ 161 chain which is itself composed of separate, thougli dif- ferently shaped, links ? The links (or the actual, inde- pendent bodies which constitute the chain) are the species ; hut the knobs, or swellings, which their several forms may tend, by degrees, to establish along its course (through the slight disparity which each of them pre- sents from that which is next in succession to it ; and therefore through the gradual manner in which the bulbs, or nodules, may be said, on the whole, to be pro- duced), are the groups into which those species naturaUy faU. assembla: be primary „„ , ,, secondary, tertiary, &c.,-in other words, whether they be departments, families, or genera, as usually understood,-the principle is in every mstance mer absolute. may !m merable strung. Now, if tliere were no sncli things as natural divisions in the organic world, these beads (which repre- mi anyhow,— their positions, with respect to each other, would under those circumstances have been of no im- portance. But such is not the case : there is an order method throughout Nature Master hand and that nothing has been left to chance. Those me ^ «tjM ^m. m I I: <(* t m 0' fi #?f 162 tudes and hues^ have liad their proper places allotted to thenij — and moreover with such care and regularity^ that _i a complete plan^ or scheme^ of distribution is at once conspicuous. Although there are not even two^ amongst that enormous multitude^ which are precisely alike (for every species^ however it may resemble its next ally^ has some distinctive feature of its own)^ we immediately per- ceive that those beads which have most in common^ are^ as it were^ attracted to each other^ — so as^ by their close approximation^ or contact^ to create excrescences and stripes^ of divers Idnds^ along the entire length of the cord- If we assume nov.^ that the red beads have been collected together^ to the length (for instance) of a yard^ and that within that space a dozen protuberances^ of discordant aspects and dimensions^ have (by the union of those beads which more nearly simulate each other) been brought about ; we shall have a very fair idea of the ordinary grouping of the animate tribes. The red beads^ taken in the mass^ may be likened to a perfect family f^ the differing gibbosities to twelve well-marked which that family includes ; whilst the (the real dramatis personcE^ of independent existence^ which are nevertheless compelled to occupy the situations we have described^ — thus causing the divi- sions to be mapped out) are here typified^ as everywhere^ by the several beads themselves. I have not thought it necessary to pursue this reason- ing into higher divisions than ^^ families ;^^ but of course it may be extended to any amount^ — so as to shadow i< ^^ genera/^ ^^ species ^^ I 163 com Nor woiild I wish to imply, by tlie above similes, that I method of arrangement Nature exist : but the mode of illustration wliicli I liave selected is applicable to all systems alike, so far as the principle is concerned. from that the terms " genus " and " species ^ not only differ gnification Whilst systematic (a position, however, wbicb depends upon the yarious structural peculiarities which it possesses in common with other beingSy more latter expresses the actual creature itself : so that while one applies to several animals (of distinct natures and though bound together by a certain bond of imrtation) , the other belongs to a single race alone, which it therefore exclusiyely indicates. But if such be the case, it will perhaps be ashed —Why then insist upon a origms t> .* C name denote all that is r ¥ may demanded for two elementary ■firsts because it is founded upon a natural truth, which (to say would because it is convenient, both for simplification and analysis. We ■*-^ #1 i ofr^^L \ n^ Hfl \sm ^ \ J^ J - 4 • ■_ ^ mt 164 ' «-^ I Kk i J, w L . to object to Ms surname^ as uniiecessary^ because be has a christian (or specific"^) one which is the exponent of him alone. True it is that his family (or generic) title applies to the rest of his kin also ; but^ since there are other people (of other families) who may have the same individual appellation as himself, it is clearly desirable^ even as a matter of expediency alone, that patronymic and christian name should be alike retained. We need not, however, plead expediency, in favour of this accept- ance of what has been so long tested, and shown to be correct ; we appeal to a higher tribunal, — that of expe- rience, — in proof that it draws its origin from Nature itself, and is implied by the very existence, or reality, of natural groups. The ^Methode Mononomique ^ has indeed been attempted f; and it has failed, — or at any rate it has shown itself to be inferior, both ideally and in prac- tice, to the plan commonly in use : and if I might be pardoned a passing conjecture on its ultimate success, I should be inclined, since it is contrary to the canon of the organic world, to regard its case as utterly hopeless. Let us not be unfair, however, towards those who have sought to establish a nomenclature which they conceived would be less open to objections than that which we have been hitherto accustomed to endorse. The notion did, * In selecting this simple method to illustrate the principle of a binomial system of nomenclature, it is scarcely necessary to remind the reader that I do not intend to imply that every man is specifically distinct from his neighbour ! t Considerations sur un Nouveau Systeme de Nomenclature^ par C. J. B, Amyot {Rev. ZooL, p. 133, a.d. 1838). nm \ } i f \ 165 w^ hole system misconce at any rate, arise out of an apparent defect in tlie bino- mial process,— for the inconveniences whicli tliey com- plained of are real ones ; and, having felt them practi- P.lUr tl^Pv asmred to sweep them away by remodellmg afresh. But, had it not been for an jtion of the generic theory, in the abstract, the trial would in all probability have never been made ; and we should have been spared the downfall of a contrivance which has had but little to recommend it beyond the ingenuity of its machinery and detail. If we analyse the motives for this experiment, we shall find that it originated from a belief, that genera are eUher purely imaginary, or else that they must (like species) have a definite and isolated existence. Now both of these conclusions appear to be equally gratuitous and could beget. ioms most naturalists will readily admit) ; but they are, like- wise, bv no means abrupt, or well-marked, on their outer limits (except indeed by accident,-of which here- mer or less slow and perceptible. Such being the case, we can easily understand why it is that the followers of the 'Methode Mononomique^ (who, paralysed by the fact that seldom clearly defined seem to repudiate them ■hiv,r,mifil svstem as in Finding that it was J possible for numerous species, whose structural charac- teristics were less conspicuously pronounced than those § K « ^\m ^\\ w * mm ¥ 'j >. \> ^ ■* ; W '^ + * y||, U i "y ^ t»2fc ^ Ilt m f 4 ■^ r- * v^ i 'Si 4 "4 N .•^ ■T +■ ^ ^ X A f^ V ■ ^ n ^^ ,^ ■ X x s ^ -Y \ ■ C'' J 166 with bility^ under two consecutive groups ; they immediately ■ inferred that the groups themselves could not be upheld on account of these connective links : and so it was re- solved (through a new and artificial scheme) to ignore them ; and to fall back upon the creed_, that species alone (and not genera) are to be recognized in the organic r world. This was but the device^ however^ at the outset^ of a single mind ; and the perverts to it have been but few. It is in direct opposition to the first principles of nomenclature^ and sets at defiance a great natural truth. But what^ it may be inquired^ is this great primary truth which the monomial system tends to violate ? I repeat what I have already stated^ that it is the existence of natural assemblages which that scheme would^ if it were practicable^ discountenance. Order and symmetry^ however (which involve classification^ or arrangement)^ are the law of Nature^ and it is not possible to set them aside. It matters not if harsh lines of demarcation are undiscernible between the several consecutive groups^ — the groups themselves must still remain (however equivo- cal it may be where they exactly commence or termi- 'J i nate)^ and cannot be wiped out. To suppose a priori that the allied divisions of the animate creation are per- fectly disconnected inter se^ is in fact to break the chain on which the unity of the organic world depends ; whilst to assume that groups cease to be groups when they can be discovered to merge into each other^ would no less destroy the harmony of that admirable method^ or 'i » 167 array, wMcli tlie naturalist, a"bove all others, delights to contemplate. If things are no longer to be regarded as their outer limits, pecial dissimilar because they unite on differences may be given up, as having no s ^ meaning, and as therefore unworthy of investigation. It requires but a slight insight into the physical universe to be convinced, that nearly everything which we see moreover^ ed into tlij tmot from Ni; venes, no man can pronounce where the one ends, and the other begins. Heat is opposed to cold; yet, if by degrees they be respectively diminished, they will at last And thus it is The sea and the land are essen- amalgamate, in a central temperature boundary is never clearly defined,— the ebb and flow are constantly and the line of separation is variable. The going on, mountain-range is moulded on a dilierent type to the level country beneath it ; yet the turning-point of them both is, in all instances, on neutral ground. We further fact. Nature most obvious. From to be detected ; not only between clusters, or material combinations, of objects (in which case it is absolute), but even between the objects themselves,— under which circumstances, however, it is merely apparent ; for, since '% ,tfV pi ■III* n i > - ^m i\ iVtlHl W I !rt: . \ V •w W V N' .^^ J ^ I I w I. -.■^' ^A i I ..^ I^J ^'V. A X vt-i4 ri ^: M 172 ' form neiglibouring group ^ venture minor ■suffice strated that, whatever be the rate, laAv, or direction, of the advancement of the various groups towards a more perfect model ; or in whatsoever position the several types immediate are to he discerned, with respect to their associates^ geneia cannot he isolated and distinct, but r 1 » must of necessity merge (each into two or more others) on their outer limits. Hence, if such be the case, as I rule contend that it usually is (the exceptions to the being, as I shall hope shortly to prove, the result of means may many im lend, both at their commencement perceptibly, with others, — their pre- cise boundaries being dimly defined. That the recognition of genera is necessary, even as a matter of mere convenience, is self-evident; for in r many extensive departments they combine with each other ) completely at their extremities (although sufficiently ell-marked in the mass), that, unless we are prepared * I may add, that this suggestion, as to the evenly balanced state generic types, is in accordance with the views of Mr. Waterhouse, whose extensive knowledge in the higher departments of zoolo- gical science gives a value to his opinion, especially on questions such as these, which I am glad to have an opportunity of acknow- ledging. \ r \ 173 to accept them as they are, we must needs repudiate them altogether : under which circumstances, our diffi- culties, both in determination and nomenclature, would be increased tenfold. We should also recollect, that clusters which seem abruptly chalked out whilst our knowledge is imperfect, are very frequently united with others when fresh discoveries are made, and the inter- mediate ffrades brought to light : so that their apparent oftentimes arise from our father than from the fact would surely be more desirable, therefore, when viewed even submit bility of a few neutral species being conceded, with equal to different groups, than to amalgamate the reason whole, and so lose sight of the general method or un questionably (in a broad sense) dispose themselves. If, however, there be any truth in the generic doctrine may omitted from our speculations in toto, — seeing that a/A (except those whose present abruptness is the effect of accident) fuse into others with which they are j genera immediate contact : m unless we ignore tliese natural assemblages from first to last, we liave no choice left ns as regards the equivocal forms ; but must consent to recognize them as of doubtful loca- tion, and as possessing an equal right to be placed m one or the other of two consecutive groups,— according [M it.i .!#* ^ itt4 \ ' ^■-*«T — I I r p \' 1 ■ ] J jiiHl * W\\ U ill. 11 1 i ! (f II II! I 1. U] if ifc ^ft ? %. MH) I t 1^ !?■'* r- 174 to the judgment of tlie particular naturalist wlio lias to deal with them. medium of an example, and endeavour to realize what would be the consequence of that wholesale combination at which must mer recede from their respective types. The immense de- partment CaraUdm, of the Coleoptera, is eminently a case in point. In the details of their oral organs the whole of that family display (as I have elsewhere"^ re- marked) so great a similarity inter se^ or rather shade off into each other by such imperceptible gradations, that the tendency which various clusters of them possess r to assume modifications of form wHcli attain their max- imum only m successive centres of radiation, must our masses wMcli the numerous species (however gradually) are, in the main, so manifestly distributed. It is possible indeed that, as our knowledge advances and new dis- coveries take place, we shaU so far unite many of the consecutive nuclei which are now considered pretty clearly defined, that we shall be driven at last either to accept the Linn^an genera only, or else the entire host of subsidiary ones (albeit perhaps in a secondary sense) which are, one by one, being expunged. And, since * Annals of Nat. Hist. (2nd series), xiv., p. 199. Hi'^ 175 ifspe would becomi from unlikely certain venient of tlie two. great genus Pterostichus, whicli lias nearly 300 representatives in Europe alone: true its several sections {Poecilus, ArgutGT, Omaseus, Coraoo, Steropus, Platysma, Molop^ opinion may from the kno Argutorsj fo] be rendered somewhat more plausible. instance) approach so closely, in their from which latter genus is turally) from scarcely distinguisliable (struc- a form which^, in its turn^ leads us on towards another type. Who im distributed groups, Calosoma and Carahus, were not thoroughly detached inter se ? yet what naturaHst now draw an exact line of demarcation And so it is with numerous others, which it is needless to recall. inference, however, from ^/ they are not homogeneous and isolated throughout, the although easily recognized in the mass, do unquestionably blend into each other ; yet I believe that it has arisen from a too rigid promulgation of the generic theory J that they have not been retained as separate. And this X 111- IDI i^'' m , I M \ I I ■, \f trtR* (t ^' t " 1 i 4i^ ^m «*«♦ Is '.■♦ 176 only ones that will remain are those which have become abrupt from causes which are merely accidental. Having now, however, examined the question in its broadest phasis, that is to say, on the supposition that Nature is complete in her several links and parts; I shaU perhaps be expected to offer a few passing words on what I have already hinted at,— namely, the possi- bility of genera being absolutely well-defined, even on om accident. Briefly, then, it is fi may^ m some instances, be abruptly expressed: but, as such contingences are at all times liable (whether from natural or artificial causes) to happen; it would be unfair to build up our generic definition from examples which are the exception, and not the rule, — and more mere ''exceptions '' (as commonly understood by that term), the result of positive disturbances from without thus occur self-evident to any one who has attempted to study the distribution of amc which have taken place on the earth's smface j for it is clear that a vast proportion of the creatures which came convulsions the positions of sea and land, apportioning to each the areas which they now embrace : so that, if generic provinces of radiation (no less than specific centres) be 1 . / \ 177 more than a fancy or romance ;m have perished for ever during the gigantic sinkmgs which have at various epochs been brought about. From '/ fi be more or less abruptly terminated, according as the original type to which they severally belong was peculiar, and in proportion as the number of its exponents has been h reduced, Altliougli tliere are many means tlirongli which species may become annihilated, yet, since the sub- maximnm ma. corollary look for islands that we should mainly look are to be rigidly pronounced. The question therefore naturally suggests itself,— Is this in harmony with what in other words, is it consistent with ex- we see; or. perience, or not ? I believe that it is ; for I think it / those groups which are more especially isolated in their most measur ! their detachment) are peculiar to countries which are \ « t * ^ ibA 1^ % i ( ^ ^ ' ^t ^ \ *^ ^i -> rfMt^^ L 3 i I :i't '/itt^ k-^jf -^.T 7 ^C r' ^ Uvv ,,u-- ^-^ / r #w 4 i; I W m insular. But, however important an element, in the eradica- tion of species, submergence may be; we must not entirely omit to notice other methods also, through the ff / f-h It r-> t5 4 I / r> ' ( f\ ■Ajf u JL / U O^,. / ( iCf * \^ ^\,jn ^ L^U /' I H \ r w '-% ru t 'fill tc> m ]kim ^ i m¥i i!)« «n> 178 medium of which genera may become well-defined. We should recollect that the removal of a very few links from an endemic cluster is sufficient to cause its dis- junction from the type to which it is next aldn^ and that where the creatures which unite in composing it are of slow diflfusive powers, or sedentary habits, the elimina- tion of such links is (through the smallness of the areas which have been overspread) a comparatively easy opera- tion. The accidental introduction of organic beings amongst others to the interests of which they are hostile, may be a powerful means, as Mr. Darwin has suggested, of keeping the latter in check, and of finally destroying them"^. The gradual upheaval of a tract which has been well-stored with specific centres of radiation, created expressly for itself, may (through the climatal changes which have been brought about) succeed in extirpating races innumerable, — those only surviving which are able to adapt themselves to the altered condi- tions; and which would now be consequently looked upon as abrupt topographical assemblages. The over- * A familiar example of this disappearance of a creature before the aggressive powers of another, which is either hostile to or stronger than itself^ is presented by the Black Rat (Mus rattus) of our own country,— which is said to have been extremely abundant formerly, but which is now replaced by the common brown (or "Hano- verian ") one of Northern Europe. The British species, however, although it has become extremely scarce, is not yet quite extermi- nated : it has been recorded {vide ' Zoologist/ 611) in Essex, and in Devonshire C Zoologist,' 2344) ; and it still swarms on a small rock off Lundy Island, in the Bristol Channel. It is reported, moreover, to have been lately re-introduced at Liverpool, . 1 i Vk .*-fcW- k^Ui^,. .-^1 1 ----- r . 1 , L 179 wtelming effect volcanic eruption, in a region where tlie aborigines of the soil have not wandered far from their primseval haunts, may- remarked from And, lastly, the intervention of man, with all the various concomitants which civilization, art, and agriculture bring in his train, is the most irresistible of every agency in the extensive (though often accidental) demo- lition of a greater or less proportion of the animate tribes. The whole of these ultimate assortments, however, are dependent, as it were, for their outline, upon contingency must from the examples which they supply. W should matter o± mere that many organic links, now absent, have, through the occurrences drawn attention, become lost. indeed common have been so ; and therefore we are induced to regard those cases as exceptional, and as in no way expository Natui tlie question, whether by the light of analogy or the more of rigid demarcation (either between genera or species, though esp"Slly the former) do not anywhere, except through accident, exist. And hence it is that we ascend. com V i If 1 1M / m i'i f !j. 180 m >y ■ t . f ir « have already glanced ; and are led to believe that, could the entire living panorama, in all its magnificence and breadth, be spread out before our eyes, with its long-lost links (of the past and present epochs) replaced, it would be found, from first to last, to be complete and continuous throughout,— a very marvel of perfection, the work of a Master^ s hand. n m fl ma i^ I m w I 1 # I I I %4t ¥-*,"- 181 CHAPTER VII. Deposita sarcina, levior volabo ad coelum.— S. Jerome. Having now completed the short task which I had undertaken to perform, I will, in conclusion, oflPer a few brief comments on the results at which we have arrived, and endeavour to realize to what extent the considera- tion of them is likely to be found useful, during our inquiries into the general subject of entomological geography . Commencin matter of experience or as probable from analogy, does ipso facto exist ; I have endeavoured to maintain that position, by evidence of divers kinds ; and I have sought to strengthen the inferences deduced, by an appeal to some of those external agents and circum- stances which may be reasonably presumed (if not indeed actually demonstrated) to have had a consider- able share in bringing it about. I have also suggested what the principal organs and characters are, Insecta, which would appear to be more peculiarly sensitive to the action of local influences ; and I have then diverged to the question of topographical distribu- tion, in connection with the geological changes on the earth^s surface ; and, lastly, to some practical hints in the m*- I i III IP. 4 m a It #4 i\& ii i; ^# ■y.* j: I I I ; ! jtat 1 4-I1 I ( fl 183 arising out of a proper interpretation of the generic theory. How far I have succeeded in elucidating the several points which I proposed to examine^ is a problem which must be solved by others ; meanwhile^ if I have failed at times to interpret what seems scarcely to admit of positive proof, I shall at least have had the advantage of propounding the enigmas for discussion, and of so paving the way for future research. We must remember, however, that, where certainty is not to be had, proba- bility must be accepted in its stead ; or, as an old writer has well expressed it : ^^ That we ought to follow pro- bability when certainty leaves us, is plain, — ^because it then becomes the only light and guide that we have. For, unless it is better to wander and fluctuate in abso- hite uncertainty than to follow such a guide ; unless it be reasonable to put out our candle because we have not the hght of the sun, it must be reasonable to direct our steps by probability, when we have nothing clearer to walk hj^^\ What my chief aim in the present treatise has been, will be easily perceived,— namely, to substantiate, as such, those elements of disturbance (on the outward con- tour of the Annulose tribes) with which the physical world does evervwhere abound : and. tbprpnr^nTi fr. r^^r^. y, whether entomologists, as a mass them into sufficient account, whei scribing as cc species y^ from distant quarters of the insects which recede in only minute particulars * Religion of Nature Delineated, p. 103. 4 r' 183 My own im from their ordinary states. they have not done so ; and, moreover, that, if they had, our catalogues would have worn a very different appearance to what they now do : for, when once the im -fi creatures is emme: conditions to which they have been long exposed. But me not he misunderstood have been thus compelled to endorse, or be supposed to ignore the fact that frequently occur in may •emoved from modifica tions of a common type. I beheve, however, that this doctrine of representation, whatever truth it may con- tain, has been too much relied upon ; and that we have been over-ready to take advantage of it (unproved as it for the multiplication of our, so called, "specific novelties.'' I suspect, indeed, that actual representative is) may more to be recognized on the isolated portions of a formerly continuous tract, than in regions which have been widely separated since the last creative epoch ; and that, in the instances where beings of a nearly identical aspect are members of them remote means) from gradually altered by the circumstances amon L IP* » *V { I m . M ^ i I f < "# m '%m '■• ti I * * ' ^■ » m. -1 I w it 4 m i f ti I #1 ( 184 they have been placed^ than that the respective phases were produced in situ on patterns almost coincident. I have before announced my conviction, that generic areas have Nature's scheme connected that, consequently, where species which are so intimately allied that they can with difficulty be distinguished, prevail, there is presumptive reason to suspect (until at least the contrary is rendered probable) that the areas which they now colonize were once intervening land, — or, in other words, that the migra- tions of the latter were brought about, through ordinary diffusive powers, from specific centres within a moderate distance of each other. I say "presumptive reason,^^ because there are undoubted exceptions to. this law (as to every other), and it can therefore be only judged of on a broad scale. Still, I contend that in a wide sense it holds good ; and that, consequently, if closely related are traceable in countries which geology " species '' durin interval since the first appearance of the present animals and plants upon our earth, there is at any rate an a priori probability that they are no species at all,— but permanent geographical states, which have been slowly matured since their casual introduction beyond their legitimate bounds. If we except those forms which are in reality but modifications, from climatal and other causes (and which have, therefore, been wrongly quoted as distinct) ; I believe that a vast proportion of the species which • \ ':t ^ * X « 4 J. Ji^ - ?- ' t M ...I I .+ I ^ s- - 1 . h ■ti ■7- i. . t' ^ In * ^' \ \ I t ■ t. * '1 ,-( - r K ^ »- ,' \ -s ..J f --c_K' /* 185 have been usuaUy considered to be "representative^^ ones^ same assem meml3ers of the self- ^ — which had wandered to a distance from their primieval haunts, and were afterwards, ,1 1 jl - „-,T .^^^ ^4? 4-1^^^ iT^foi^Trf^nTnor land. CUt ■m intervenin from I have adduced, in a preceding chapter, some remarkable illustration of this hypothesis,— an hypothesis which I believe to be the true clue to a very large item of the ^ ^^ specific representation ^^ theory. Madeiran Helices may >#i number LtL^^"^ (which I have akeady may i mainl that it is to island groups that we must would resign in toto the doctrine of " specific representation," even as frequently understood (that is to say, as recog- nizable in countries which have been altogether dis- connected since the last creative epoch) , and therefore, a fortiori, in wbat I conceive to be its truer meaning ; there is yet another point on which I would desire to be interpreted aright, whilst endeavouring to substantiate member insect It has been aim im circumstances " and conditions in regulating, within defi- nite limits, the outward aspect of the Articulate tribes. * Vide supra^ p. 128. A^ a } \ I done ^) as, in the strictest sense, representative of each J^ other,-and as therefore specifically distinct : and I r 14 M M • t —I*^- ^ 186 k*. ti it 'I- »1 ^in I i '^ 4i^tei 1i] 4 «< I" ! ' W4f' «l « I f « « I i I do not^ however^ assert that every species is liable to be interfered with ab extra ; that is a question which the greater or less susceptibility of the several races^ as originally constituted^ can alone decide ; still less would I willingly lend a helping hand to that most m ischievous of dogmas, that they are ^//-important in their opera- tion, — or, in other words, that they possess within them- selves the inherent power (though it may not invariably be exercised) of shaping out (provided a sufficient time be granted them, and in conjunction with the advancing requirements of the creatures themselves) those perma- nent organic states to which the name of species (in a true sense) is now applied. Such a doctrine is in reality nothing more than the transmutation theory, in all its unvarnished fulness ; and I do not see how it can be for a moment maintained, so long as facts (and not reason- ing only) are to be the basis of our speculations. I repeat, that it is laerelj within fixed specific bounds that I would advocate a freedom of development, in obedi- ence to influences from without : only I would widen those limits to a much greater extent than has been ordinarily done, — so as to let in the controlling prin- ciple of physical agents, as a significant adjunct for our contemplation. It does indeed appear strange that naturalists, who have combined great synthetic qualities with a profound knowledge of minutiae and detail, should ever have upheld so monstrous a doctrine as that of the transmis- sion of one species into another, — a doctrine, however^ I ^^ f h^jl^ u 1. ^r4 J*; M >-■' ih -4Al^ 'J .tH. ir H r .» i^ ^ \ji (P f,'.^ I r ( _ -^ 187 assume wMcli arises almost spontaneously,— if we that there exists in every race the tendency to an un- limited progressive improvement. There are certamly no observations on record which would, in the smallest degree, countenance such an hypothesis , Many modifi- ancl pianxs, It is nut;, arc uajjauxo wx ^^.^-k. cations and changes, for the better —very much more than is the case with others. But what does this prove. .ncement wider compass It touches not moreover the fact, that the boundaries of their respective ranges are absolutely and critically defined. It is singular pha^nomenon, and one in which th. ^^xu^g... proofs of design (or a primary adjustment of limits with a view to the futm-e) may be discerned, that the mem- bers of the organic creation which display the greatest adaptive powers, are those which were apparently des- peculiarly attendant upon man The best-authenticated examples," says Sir Charles Lyell, '' of the extent to which species can be made to vary may be looked for in the history of domesticated animals and cultivated It usually happens that those species which have the greatest pliability of organiza- most themselves to a great \i most serviceable to man him into These only can be carried by have their pro- climates, and can perties or instincts variously diversified by differences of nourishment resources / t. / f *»< * %4 w -4 \'- ']ii '( *#l^ MM J V ';fM ii i mm |i * I I. \ .if- m »i I ij^ > I f UM f l« irl *■! * ■i mtr I! li 4 m^ti i 9^ ' 'rf *v -i> 188 be so limited, and its habits and faculties be of such a confined and local character, that it can only flourish in a few particular spots, it can rarely be of great utHity . We may consider, therefore, that in fliP rl^^..+;„„^- J animals most frames and constitutions, and have then been engaged for ages in conducting a series of experiments, with much patience and at great cost, to ascertain what may be the greatest possible deviation from a common type which can be elicited in these extreme cases ^." The fact, however, that all areas of aberration (how- ever large they may be) are positively circumscribed, need scarcely be appealed to, in exposing the absurdity of the transmutation hypothesis. The whole Theory is full of inconsistencies from beginning to end ; and from whatever point we view it, it is equally unsound. How, for instance, can any amount of local influences, or the progressive requirements of the creatures themselves, / give rise to the appearance of several well-marked re- presentatives of a genus on the self-same spot,— where the physical conditions for each of them are absolutely ^^T same ? Look, for example, at the Tarphii (to which Vtti alluded t) of Madeira ^^'"1^^^ ^"^""^K ^^^''^^'^ abundantly defined species; and. ♦■ u vM /^r o - „ ^j ^^iiiicu species; and, as stated in a previous chapter, I have but little doubt ^! I V^ Iff i/ |v ^ (I \ I r f I e\ h ^ ^ ^-^ * Principles of Geology, 9th edition, pp. 583, 584. ^/^ ^ ^ I f f « t ir / # '^ (p^ y m r i I ">*,, r_"- ^ -"^ Fx ^ /"' \i/m 189 djusted in which they obtain, that they are strictly an esoteric assemblage, inhabiting the actual sites (or nearly so) of their original debut upon this earth. Here, then, we have a sufficient leu taken place; they are all exposed to the self-same agencies from without (for they live principally in com- munion) ; yet, though I have examined carefully more than a thousand specimens (a large proportion of them beneath the microscope), I have never discovered a single intermediate link which could be regarded as in a transition state between any of the remainder. But r how is this ?— Is it possible to account for differences so decided, yet each of such amazing constancy, amongst the several creatures of a central type which have been exposed to identical conditions through, at any rate, generations innumerable? They clearly cannot be ex- ,^ioir.prl nn thft flnctrine of transmutation : yet they are rule occupymg an ana- • logons position to the members of every other endemic group. . But I will not occupy more space on the transmuta- tion theory : suffice it to have shoT^oi that, in thus con- ceding a legitimate power of self-adaptation, in accord- ance with external circumstances, to the members ot the insect world; and in suggesting the inquiry, whether the action of physical influences has been adequately allowed for by entomologists generally (or, in other words, whether the small shades of difference which ;'iM it* iM /^ i* 't^m \ <«» 191 ably not. Trutli is truth, under wliatever aspect it may and cannot possibly contradict another truth. ellectual faculties, by tracing out, come; our m m even a single natural law, is an honourable task ; nor should the apparent smallness of the media which we are at times compelled to employ, render it less so (else would this present treatise, like many others of a kindred stamp, have been best unwritten) : but it is from the wn im more to be anticipated. An effect may be literally dependent upon a certain proximate cause ; and if we be so fortu- nate as to ascertain that cause, we have done somethmg ; but it does not necessarily follow that we have done much. On the contrary, it often happens that, in so doing, we wonderfally may seeing that the pro- Behind that "cause,^^ we should recoUect, others lie concealed, of a far deeper nature, each depending upon the next in succession to it ; until, in the order of causation, we are at length led back, step by step, to the Einal One,-with which alone the mind can be thoroi covery after discovery. We make }} Whewell C( m the ory. 1 and in itself complete, but none final. Somethmg always remains undone. The last question answered, the answer suggests still another question. The strain of music from the lyre of Science flows on, rich and m m t » Mi* i '. i* iiU i ill t i i ■' M f i *» iVft .<^ Bill (*^ n ^ I I t4i ) I *f« h' H in mil M If f 111 ♦ * M H tt« ^f »* 192 sweety full and harmonious ; but never reaches a close : no cadence is heard with which the intellectual ear can feel satisfied^." obscure >/ the point. It frequently happens indeed that even observation itself is insufficient to render the lines of demarcation inteUigible, — therefore^ how much more mere dialectics ! To attempt to argue such a subject on abstract principles^ would be simply absurd ; for, as Lord Bacon has remarked^ ^^the subtilty of Nature far exceeds the subtilty of reasoning : ^^ but if^ by a careful collation of facts y and the sifting of minute particulars gathered from without, the problem be fairly and deli- berately surveyed, the various disturbing elements which the creatures have been severally exposed to having been duly taken into account, the boundaries will not often be difficult to define. Albeit, we must except those races of animals and plants which, through a long course of the starting- become points of which will perhaps continue to the last shrouded in mystery and doubt. It would be scarcely consistent indeed to weigh tribes which have been thus unnaturally tampered with by the same standard of evidence as we require for those which have remained for ever un- touched and free, — especially so, since (as we have already observed) it does absolutely appear, that those species, the external aspects of which have been thus artificially con- * Indications of the Creator (London, 1845), p. 163. mi \ «*" /• 193 II ta^ 1):| I « I \ ■■ I. \ I 4 .t more thereiore^ more rest. Whether .■-> this circumstance^ ^r whether those forms were originally i^^-^^*-^' ^>>' >/ me to conjecture ferences is the one which I should, myself, be a priori ^ inclined to subscribe to. In examining, howe^ this enigma, of limits within which variation is (as such) to be recognized-, it should never be forgotten, that it is possible for those boundaries to be absolutely and critically marked out even where we are not able to discern them : so that the difficulty which a few domesticated creatures of a singu- unneces sarily predispose us to dispute the question in its larger and more general bearings. Nor should we be unmind- ful that fas Sir Charles Lyell has aptly suggested) ' some mere many individuals may dilemma But, whatever be the several ranges within which the members definition of as involving relationship^ he more than a delusion or ro- mance, their circumferences are of necessity real, and must be indicated somewhere, — as strictly, moreover, and Nature K ^f \ ¥ 4 4 i -im* ■ « ? II iw I <4« 111 M m h*i r i r .1 1 1 -i 'J i ■ i . fliH :kii I *■ vrf 194 chalked out. The whole problem^ in that case, does in effect resolve itself to this, — Where, and how, are the lines of demarcation to be drawn ? No amount of incon- stancy, provided its limits be fixed, is irreconcilable with the doctrine of specific similitudes. Like the ever- shifting curves which the white foam of the untiring tide describes upon the shore, races may ebb and flow ; but they have their boundaries, in either direction, beyond which they can never pass. And thus in every species we may detect, to a greater or less extent, the emblem of instability and permanence combined : al- though perceived, when inquired into, to be fickle and fluctuating in their component parts, in their general outline they remain steadfast and unaltered, as of old. (6 Still changing, yet unchanged; still doom'd to feel Endless mutation^ in perpetual rest,'* I I t 1 i ( I . _ ^ J- •> — ■ *^ JPiT- INDEX. \n r Aberration, perhaps indicated universally, 16, 17, 18. Aborigines, insect, unimportant for climatal modifications, 25, 26, 27- JcaHes, the Canarian type of, apparent on the Salvages and De- zertas, 124. ^ . .,7 \ toa Neptunus, WolL, perhaps a state of J[^. arffillosus, 124. Achatina Eulima, Lowe, its extinction in Porto banto, idl. Adimonia, the capture of, out at sea, 150. Aepus marinus, Strom., paUid hue ot, 0^. Robinii, Lab.,palUd hue o^ 64 y .^ oi Agabus bipustulaUs, Linn., unaffected by climate, 6i. Alligators; their peculiarity to S. America, 14 J. Alpine species, some peculiarly so, 4U. Altitude and latitude, sometimes reciprocal, d5, 114. Amycterus, its concentration m Austraha, I4d. Amvot M., his ' Methode Mononomique, lb4. Analogies, Lord Bacon on the importance of, 13 ; why necessary to be studied, 14. , n n i o Analogy, argument from, iU, H, i^- tit :i • „ q«i AncUmenus marginatus, Linn., shghtly modified m Madeira 38^ Andes, dissimilarity of the fauna on the opposite sides of the, 14(x Anobium striatum, Oliv., unaffected by climate, dl. AntenuEB, joints of, said occasionally to vary, 96. Anthicus bimaculatus, lUig., variabihty of, near the sea, do fenestratus, Schmidt, shghtly modified m Madeira, oo- humilis, Germ., variability of, in salt places, bd. . instabilis, Hoffm., pallid hue of, 64. j p;q 7q Anthonomus ater, Mshm, very small in Lundy ^^^J^'^^ f^^ Aphelocheirus cBstivalis, Fabr., the hemelytra of, sometimes tuiiy AphoiTnVcMus, Fabr., paler in Madeira than in Europe gene- rally, G5. ^2 !) < IH« !' \\M m r IS > t i •M i ^ 196 INDEX. )■ \ tu i i: fiA^i l»ftr It'ii I ^ ApTiodius plagiatus, Linn., usually black in England, 61 ; two distinct states of, indicated, 105. ApocyrtuSy its concentration in the Philippine Islands, 143. Apotomus, common to Madeira and Sicily, 139. Argutor, always apterous in Madeira, 82; trophi of, almost iden- tical with those of Calathus, 175. Armadillos, their peculiarity to S. America, 143. Armitage, Mr., onCicindelafasciatopimctataf}:omM.onnt 01ympus,4 1 . Arrangement, a lineal one is not indicated in Nature, 163. Atlantic continent. Prof. E. Forbes on the former existence of, 137. Atlantis of the ancients, the impossibility of its being identified with a former Atlantic region, 140 ; perhaps the New World, 141. Atlantis, the genus, a modification of LaparoceruSy 143. Azores, the colonization of, by two Madeiran Helices^ 133. Bacon, Lord, on the importance of analogies, 13; on the Atlantis of the ancients, 141 ; on the necessity of observation for forming science, 159, Banksias, their concentration in Australia, 142. Barriers, natural, the difiference between primary and recent, 145 ; their hindrance to insect diffusion, 145. Bembidium Atlanticuniy WolL, paler in Porto Santo than in Ma- deira, &Q ; the variations to which it is subject, 107, 108. bistriatuMy Dufts., paler in saline districts, 62. epMppium, Mshm, pallid hue of, 64. obtusum, Sturm, varies in southern latitudes, 33. pallidipenne, Illig., pallid hue of, 64. saxatile, Gyll., variety of, on the south coast of England, 60. Schmidtii, WolL, perhaps a state of 5. callosumy 66. scutellare, Germ., pallid hue of, 64. tabellatum, WolL, perhaps a state of B. tibiale^ 66. Berginus, common to Madeira and Sicily, 139. Black Rat, nearly exterminated in England, 178. Blemus areolatus, Creutz., paler in brackish places, 62. Bolitochara assimilis, Kby, smallness of, in the Scilly Islands, 73. BoromorphuSy common to Madeira and Sicily, 139. Brachinus crepitans^ Linn., two distinct sizes of, frequently indi- cated, 105. Brady cellus fulvus, Mshm, apterous in Madeira, 85, Bread-fruit Trees, their peculiarity to the South Sea Islands, 142. Calathus, apterous in Madeira, 82; its trophi almost identical with those of PristonychuSy 175. complanatus, KolL, vai'iesfrom altitude, 39; variety of, on one of the Sladeira Islands, 88. fuscus, Fabr., slightly modified in Madeira, 38, 85. \ 1 ■ 4 ^ r I INDEX. 197 Calathus melanocephalus, Linn., smallness of, in the SciUy Islands, 73 'mollis, Mshm, variable in its wings, 43 ; lurid colour of, 64. Calcareous soils, effect of, on the aspect of insects, 66. Calceolarias, their concentration on the Andes, 142. Calosoma, a species of, ten miles from shore, 147 ; the genus, meiges gradually into Carabus, 175. \_ Syncophanta, Linn., its power of crossing the sea, 14/. Canary Islands, migratory direction of their insect population, 1 iy. CarabidcB, inconstant in their organs of flight, 43 ; family ot, nearly similar throughout in its oral organs, 17 A. Carpophilus hemipterus, Linn., unaffected by climate, dl. Cmllotrupis conicollis, WoU., large size of, on one of the Madeira Islands, 88, 109. on mo lucifugus, Woll., varies from isolation, ^^^^ ^ Causes, never final ones which we investigate, 19 1 . Centrinus, its concentration in S. America, i4d. Ceutorhynchus contractus, Mshm, smallness of, m Lundy Island, 59 73. Cholovocera, common to Madeira and Sicily, 139. Westw if< Chrysomela, apterous in Madeira, 82. ChrysomelcB, vary from altitude, 41. ChrysomelidcB, almost absent in Tierra del Fuego, 4/ . Cicmdela fasciatopunctata, Germ., a state of C. sylvatica, 41. Cicindelidce, often variable, 41- Cillenum laterale, Sara., Innd hue oi,b4. _ Cmea; ajo^ems, Linn., the development of the wings of, 100. lectularius, Linn., on the development of the wmgs ot, .5. Cistela sulphurea, Linn., its variability near the sea 60 Clausilia deltostoma, Lowe, a Porto-Santan form of, 134. Climatal modifications significant, although small, 42 Chmate, not important as a disturbing cause, 23, 24, 31, d^, 4Z. Clouded-yellow Butterfly, unaffected by chmate, 31. Clypeaster pusillus, Gyll, differs sUghtly m Madeira, 6o. Coast, inconstancy of insects in the vicinity of the, 57- Coccinella 7 -punctata, Linn., unafi"ected by chmate, 31. Colias Edusa, Fabr., unaffected by climate, 31. Colour, its inconstancy in insects found near the sea, o/, o». of insects, affected by isolation, 88. no i f;ri Colvmbetes, a species of, captured forty-five milesfrom shore, 14^,1^ Compensation, generally apparent when an insect is deprived of an orffan or sense, 81. . ^i* mi Cormus subapterus, Curt., the development of the wmgs of, 101. Cordillera, Mr. Darwin on the fauna of the, i4i). iH in ii *( » ' 4 ^ . .^ 198 INDEX. f I »4> 6.', I m t iir KMl4 »»>« # I Corylophus, apterous in Madeira^ 82. Criomorphus, Curtis, referable to the genus Delphaw, 45. Cyclostoma lucidum, Lowe, its extinction in Porto Santo, 131. Cynthia Cardui, Linn., unaffected by climate, 32. Cynucus, a species of, seventeen miles from shore, 150. Cyrtonota^ its concentration in S. America, 143. Darwin, Mr., on the fauna of the Galapagos, 23; relative propor- tions of the insect tribes in the tropics, 28, 29 ; on the insects of Tierra del Fuego, 47 ; on the natural features of Tierra del Fuego, 50; on the insects of Keeling Island, 55; on the insects of St. Helena, 55 ; on the insects of Ascension, 55 ; on the apterous condition of insular species, 86 ; on the fauna of the Cordillera, 145; on a Calosoma captured at sea, 147; on insects captured in the sea, 149, 150; on the disappearance of animals before more powerful ones than themselves, 178. Dawson, Rev. J. F., on a variety of Bembidium saxatile, 60. Definition of the term ' species,^ 4 ; of the term ' variety,' 4. DelpJiax, on the development of the wings of, 45. Dermestes vulpinus, Fabr,, unaffected by climate, 31, Deucalion^ its occurrence on the Salvages and Dezertas, 125. Desertarum, WolL, its sedentary nature, 125, 126, 127- Dichelus, its concentration in S. Africa, 143. Differences, when to be regarded as specific, 6 ; too exclusively studied, 12. Diffusion, various means of, which operate on the insect tribes, 148. Disturbing agents, Prof. Henfrey on, 8. Ditylus, the same type of, indicated in the Canaries and Salvages, 124. Domesticated animals, pliable nature of, 187, 192. Dromius arenicola^ WolL, representative of D. obscurogtcttatuSy 66. fasciatus, Gyll., its paleness near the sea, 63, negrita, WolL, perhaps an ultimate state of D. glabratus, 85. obscuroguttatus, Dufts., its changes in Madeira, 36, 37, 38 ; apterous in Madeira, 84. — sigma, Rossi, its colour affected by isolation, 88, 89. Elevation, sometimes corresponds with latitude, 35, 114. EUipsodes glabratus, Fabr., singular variety of, on one of the Ma- deira Islands, 88, 109. Elytra, connateness of, a variable character, 96. ' Endemic,' to what species the term is appHcable, 118. Entomology, the study of, does not necessarily cramp the mind. 111. Ephistemus, apterous in Madeira, 82, Eucalypti, their concentration in Australia, 142. Eunectes sticticuSy Linn,, unaffected by climate, 31. • Euphorbias, their concentration in Southern Africa, 142, i I r K 1 I INDEX. 199 Eurygnathus Latreillei, Lap., variety of, on one of the Madeira Islands, 88, 109. . ^ -. Exceptions, not be allowed to negative a law /A /o. Extinction of species, as indicated m the f^^'^f^^ZTm ' the only cause by which genera may be abruptly dehnea, i / u. Forbes, Prof. E., on the origin of the British animals and plants 130 : his epochs of migration of the British animals and plants, 136 ; on the existence of a former Atlantic continent, id/ . Forests, the hindrance which they oflPer to insect-dittusion, io-i. "Fortunate Islands" of the ancients, probably the Canarian group, 141. nation of, 160, 161, 162; cannot be abrupt 'f.'^P'^X situated 169; how to be defined, 169; tlie types °f • •'™^ '^ *'\"f 5' towids the eentres of a-^^S^urJcha a"Sf a *l-y area of diffusion, 1.0. Gerris, on the development of the wmgs of, 100. Gould, Mr., on the Swallows of Malta, 102 Gymnaetron, blood-red dashes characteristic o^ 62. ^ Campanulce, Linn., its smallness on the Cornish coast, o8. VeroniccB, Germ., a variety of G. niger, 62. Hadrus illotus, WoU., perhaps a form of H cinerascens, 66. Haliplus obUquus, Gyll., dark state of, m Ireland 6/ . Haltica exoleta, Fabr., its variability on the coast o9. Harcourt, Mr., on the discovery of Madeira, 49, 50. Harpalus vividus, Dej., changes to which it is subject, 67, 68, 6J, variable in the connateness of its elytra, 96, y/. Hegeter, its maximum attained in the Canaries, i^u. _ — do^^a^t*., Oliv., its migration from the Canaries, 120, ot more adaptive nature than its allies, 121. „ ion latebricola, WoU., its occurrence in the balvages, i^^. Helices, have often two distinct states 10 ; many of ^^^^^ -pi- sentative m the Madeira Islands, l2o, 1^^ > ^^^^"""^ chiefly of slow migratory powers, 130, 131. Helix attrita, Lowe, its local character, 132. nvnctulata Bowdichiam, Fer., perhaps a gigantic state of H- i^^eA/,cf.Uara, calculus, Lowe, sedentary nature of, 132. in h«^ R 1 = U H H i \ M .3 1 - 1 i '"^-1 • f i m ft « 1 i ' !t tl 1 fw i 1 ii I I «* Ifli^ tin lil 9 S 200 INDEX. Heliiv commiwta, Lowe, sedentary nature of, 132. coronata, Desh., its peculiarity to Porto Santo, 128; its occur- rence beneath the surface of the ground, 131. coromda, Lowe, its peculiarity to the Southern Dezerta, 128. — Delphinula, Lowe, the Madeiran representative of H. tectifor- mis in Porto Santo, 129. — discina, Lowe, a form of H. polymorpha, 133. erubescens, Lowe, its powers of diffusion greater than those of its aUies, 133; sensitive to external influences, 134. Jliwtuosa, Lowe, its extinction in Porto Santo, 131. hirsuta, Say, two distinct states of, 106. lapicida, Linn., its extinction in Porto Santo, 131. — latens, Lowe, the Madeiran representative of H, obtecta in Porto Santo, 129. — lincta, Lowe, the common Madeiran form of H. polymorpha, 104. — Loweiy Pfr., perhaps a gigantic state of H. Portosanctana, 106. — papiliOy Lowe, a form oi H. polymorpha^ 133. — paupercula, Lowe, its powers of diffusion greater than those of its allies, 133. 7 great diffusive powers, 133. Portosanctana, Sow., its peculiarity to Porto Santo, 129. — pulvinata, Low^e, a form of H. polymorpha, 133. — saccharata, Lowe, a local state of H, polymorpha, 134. — senilis, Lowe, the Dezertan form of H, polymorpha, 134. — squalida, Lowe, the Madeiran representative of H. depauperata in Porto Santo, 129. tiarella, Webb, its sedentary nature, 128. undata, Lowe, its peculiarity to Madeira proper, 129. Vulcania, Lowe, its peculiarity to the Dezertas, 129. Wollastoni, Lowe, sedentary nature of, 132. Helobia nivalis, Payk., perhaps a state of H. brevicollis, 40. Helops, always apterous in Madeira, 82. confertus, WolL, varies from altitude, 39. futilis, WolL, varies from isolation, 109. testaceus, Kiist., pallid hue of, 64. Vulcaiius, WolL, large size of, on one of the Madeira Islands, 88. Henfrey, Prof., on disturbing agents, 8. Herschel, Sir John, on the requisites for an observer, 12, Hipparchia Semele, Linn., has a distinct aspect in Madeira, 34. Hipporhinus, its concentration in S. Africa, 143. Holme, Mr., on Olisthopus rotundatus in the Scilly Islands, 58, 102; on a winged state oi Phosphuga atrata, 102. Holoparamecus, common to Madeira and Sicily, 139. niger, Aube, different in Madeira and Sicily, 33. T > t INDEX. 201 Hooker, Dr., on the insects of Kergue en s Land, 86. Humboldt, his notice of Sphinxes and flies high up <>^ ^J^^^^^^j'^ Humming-Birds, their pecuUarity to S. America and the W • indie., Hydrobius, apterous in Madeira, 82; the capture of, out at sea, 150. HydrometridcB, on the development of the wmgs ot, luu. Hydroporus, the capture of, out at sea, 150. ■ confiuens, Fabr,, unaffected by climate, 31 . Hypsonotus, its concentration in S. America, 14d. r Influence of climate not important, 23. ^^ ^^ ^a Insect-aberration, perhaps a universal fact, lb, ^^ ^^- Ins^Fortuna,. of Juba W^-^^ ^^^ ^'^l^^J^^'^^^ has Ireland, poverty of the fauna ot, OJ, oo , tuc something in common vvith Madeira, 1^^; ^ ^neoies of Islauds, tauL of, often f^.^-^^rrStl^'o^^r^^^^^^^ generally more isolated m tneii suut^tui^ 177. Isolation, effects of, on insect-stature, 71. Ixias, their concentration in Southern Africa, 14.. Kangaroos, their concentration in Austraha, 142. Kerguelen's Land, insects of, Hb. a„ffnlk roast Kirby, Rev, W., on insects washed up on the Suffolk coast, L.uopM<.us pusillus Schbnh --^^^^^^^^^^tt"?^^^^ Lamprias chlorocephalus, Ent. H., two distinct sizes oi, 11^4 indicated, 105. . , , • f ^^ one of the Madeira Laparocerus mono, Schonh., large size or, on one ui Islands, 88. . • ^„i qc T atitnrlp and altitude, sometimes reciprocal, 6t>. t ^ 7 • Lm^r, its peculiarity to Madagascar, 143. Litargus, common to Madeira and bicily, IJ^. Li^ws angustatus, Fabr., unaffected by climate, di. Localities, some naturally more productive than others W, • Longitarsus, the native species of, apterous m Madeira, oz. Loncem, apterous in Madeira, 82. „w„r„™ 127 Lowe, Rcv.'r. T., his capture of ^--^-^ ^57:^ruT;enceof the Lundy Island, smallness of the insects in, 58, b)J , occuixc Black Rat in, 178. . T?^„in^^ qa Lj^c«..a PM(Ba., Linn., darker in Madeira than ;^ Eng^'^' ^f^"^ ^f Lvell, Sir Charles, on Helix Ursuta, 106; «« ^J^ ^^^^^^ the shore -the Madeiran H.Zice., 129 ; on ^^^^^^s washed up c^a the shore, 148 • on the effect of gales in the transportation ot msects, 14» , 147 \ V #- f I [ 4 1 i \ i i ii \ r i^^'U ft' f -\ 202 ■^ INDEX. on the effects of a volcanic eruption in destroying species, 179 ; on the flexible nature of certain animals and plants, 187; on the greater differences which varieties often present than do species, 193. hygmus hrevipennis, Latr., on the development of the wings of, 101. » I r \ I Macronota, its peculiarity to Java, 143. Madeira, has some features in common with Tierra del Fuego, 48, 49, 50, 51; former state of, 48, 49; great fire on the southern side of, 49; origin of the name of, 50; the insects of, 55; the tendency of its insects to become apterous, 82 ; the migratory direction of its insect population, 119; the local nature of its various species, 152, 153. Magnolias, their concentration in Central America, 142. Malta, Mr. Gould on the birds of, 102. Malthodes Kiesenwetteri, Woll., perhaps a state of M, brevicoUis, 66. Man, agency of, in the destruction of species, 179. Mantura Chrysanthemiy Ent. H., variability of, in Lundy Island, 59. Marsupialiay their concentration in Australia, 142. Mesembryanthemums, their concentration in Southern Africa, 142. Mesites, a modification of Cossonus, 144. Maderensis^y^oM.y its near relationship to the M, Tardii, 141. Tarda, Curtis, its variability near the coast, 58. *Methode Mononomique,' the unsoundness of, 164 — 168, Migratory powers, slowness of, in the Madeiran Helices, 130 — 132. progress, direction of, in the Madeiran animals, 120, 135. Mimosas, their concentration in Austraha, 142. MoUusca, Terrestrial, often present two distinct states, 106. Moluris, its concentration in S. Africa, 143. Monochelus, its concentration in S. Africa, 143. Mountain-chains, their hindrance to insect-diffusion, 145. Mountain-tops, either very prolific in insect life, or else barren, 115. Mus Rattus, almost extermmated in England, 178. Mycetoporus pronus, Erichs., two distinct states of, indicated, 106. Myrtles, their concentration in Australia, 142. r Naturalist, the, what his province to investigate, 158. Nature, not irregular because presenting occasional anomahes, 94. Naupactus, its concentration in S. America, 143. Nebria complanata, Linn., unusually pale near Bordeaux, 33 ; pallid hue of, 64. New World, some of its insects perhaps but states of those of the Old, 37. Nomenclature, a binomial system the only true one, 164, 168. Notaphus, the capture of, out at sea, 150. Notiophili, extremely variable, 40. ] A INDEX. 203 NotiopMlus gemnatus. Dej. large size of, on one of the Madeira Islands, 88. Observation, indispensable in natural science, 20, 159, 192. Ocean, the, its hindrance to insect-diffusion, 14o. Ochthebius marinus, Payk., lurid hue ot, b4. Olisthopus, apterous in Madeira, 82 . , ^ n ,i, ^ >Ti d eira Islands , - ' lerensis, Woll., large state of, on one of the xMadeira isiauu , ^^- rftundatus, Payk., very small in the Scilly Islands, 58, 73 ; subapterous in the Scilly Islands, ]02_ Omaseus nigerrimus, Dej., a form of 0. frrimus 33 Omias Waterhousei, Woll ' '"'^ '^^ "" ""« "* Islands, 88, 109. „ , . ^ mi Oncocephalus griseus, development of the wmgs ot, lui. O^Ams, apterous in Madeira, 82. t i„v^rl= 14S Ourangs, their peculiarity to the Indian Islands, 14d. Oxyomus, a modification of Aphodius, 144. Paclyn^erus Irevipennis, the f.-^ThTklp^^^^^^^^^ PacJiyrJiynclus, its concentr^ion ^^^^e rnuipp Painted-Lady Butterfly, ^'^^^^'^^f^'lfT^l % Papilio Maciaon, Linn., unaffected by c mate, dl. Paropsis, its -^ru^^f^^^^^^'l^Z ^f Tierra del Fuego, 47, 48. Patagonia, insects _of,_distmct ^^^^e^^^^ to be a state of P. Patrobus septentrionis, Dej., nas oeeu s>uppu= excavatus, 40. . 4.i,„ Po,-,ov;p« 124 Pecteropus, its maximum attained m the Ca^anes, 124. Maderensis, Woll., varies from altitude, dy. rosfratus, Woll., varies from isolation, ^U. Pelare^oniums their concentration m Southern Africa, 142. S;Sr;«/i., Payk., larger in Ireland than m the Orkneys, 33. Phaleria cadaverina, Fabr., P^ ^^^i hu^ f ^^f ^^ f^,^ ^ly indicated, Philhydrus melanocephalus, Oliv., two states oi, iiequLui y 105. ^ Phlmophagus , apterous in Madeira, 82. _ i^^^inripd 102. PhospMga atrata, Linn., taken with the wings developed 1U-. suhrotundata, Leach, the Irish form of the P. «^raf«, Phytophaga, preponderance of, in the tropics, 2»,^y. PierisBrassiccB, Linn., varies in Nepaul and Japan, J4. Pissodes notatus, Fabr., unaffected by chmate d^- Platyomus, its concentration m S. America, i^-^- Platyrrhini, their peculiarity to S. America I4d. Pogonus luridipennis, Germ., lurid hue ot' «^- probablv re. Pontia BrassiccB, Linn., its introduction mto JViadena pioD y cent, 74. I 1 \ \ i I i 204 INDEX. I [|tf m f y^ m ***