ALBERT R. MANN LIBRARY AT CORNELL UNIVERSITY DATE DUE | ity Li n of species, with especia iii _ QH | On the variatio wh 1924 i Cornell University Library The original of this book is in the Cornell University Library. There are no known copyright restrictions in the United States on the use of the text. http://www.archive.org/details/cu3 1924003056987 ON THE VARIATION OF SPECIES WITH ESPECIAL REFERENCE TO THE INSECTA; FOLLOWED BY AN INQUIRY INTO THE NATURE OF GENERA. BY T.”" VERNON WOLLASTON, M.A., F.LS. “No compound of this earthly ball Is like another, all in all.’’ TENNYSON. LONDON: JOHN VAN VOORST, PATERNOSTER ROW. 1856. “‘T 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, I care not from what term the d tration or arg’ t takes its rise. Either way propositions may beget their like, and more truth be brought into the world.’’— Religion of Nature Delineated, p. 45 (A.D. 1722). PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET. TO CHARLES DARWIN, Esq., M.A., V-P.BS., Whose researches, in various parts of the world, have added so much to our knowledge of Zoological geography, this short Treatise is dedicated. CORNELL UNIVERSITY : LIBRARY PREFACE. 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- ing 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 v1 on the volume a more practical interest, for the general naturalist. 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 great questions arising out of the distribution of animals and plants; hoping that, by so doing, some few of our 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 brought 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. 10 Hereford Street, Park Lane, London, May 10th, 1856. CONTENTS. CHAPTER I. Page Introductory Remarks .....0..........00..00.0:ccccccceeeeeeeees 1 Fact of Variation ......0.0....00 coc cee ccc cece eee eer eevee 7 As a matter of experience .....c.cccssseecseeeeeeeeeeeneees 8 As probable from analogy ........sscesccsneesececeeseeeees 10 CHAPTER III. Causes of Variation .......00..0... ccc ccccec cee cee cee cee tec cee ees 19 § 1. Climatal causes generally (whether dependent upon latitude or upon altitude) ............0.26 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 CHAPTER IV. Organs and Characters of Variation ............0....... ... 95 CHAPTER V. Geological Reflections ...........0..0 0 eee 111 CHAPTER VI. The Generic Theory............ 00.0.0 cccee eee cee 157 Conclusion. «.oc5 oa decoscin ativan nat Re Bk eae 181 CORRIGENDUM. Page 90, for Pecteropus Maderensis read Pecteropus rostratus. SPECIFIC VARIATION IN THE INSECTA. CHAPTER I. INTRODUCTORY REMARKS. A very small amount of information gained by the student in the field of Nature is sufficient to kindle the 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: 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, Truth, “at the bottom of the well,” is assuredly present, under some form or other, to reward him still; 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 2 of what she ought to be. In these times of patient re- search, when the microscope is disclosing, day by day, fresh wonders to our view, and new lines of speculation are springing out, as it were spontaneously, from the regions of thought, it is remarkable that many of the commoner questions relating to the members of the external world around us have remained comparatively unsolved ; nor indeed have some of them ever been dis- cussed at all, except m 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) of the animal kingdom stand pre-eminent,—especially in the Annulose Orders, in which those distinctions are less easy, & priori, to pronounce upon. The descriptive naturalist, whose primary object it is to register what he sees (apart from the obscurer phe- nomena which come within the province of the more philosophical inquirer), can have scarcely failed to re- mark the variation to which certain insects are at times liable from the external agencies to which they have been exposed: and yet, in spite of this, it is but too true that even physiologists have frequently shunned the in- vestigation of the circwmstances on which such varia- tions do manifestly in a great measure depend, as though they were in no degree accountable for the changes in question, and did not indeed so much as exist except in theory. In the following pages I purpose, inter alia, to throw out a few general hints ; first, on the fact of aber- 3 ration, as a mere matter of experience; and, secondly, on some of the causes to which 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 be inclined to dispute: and yet it is abundantly evident that it cannot be taken into account, at any rate satis- factorily, without involving the Jatter 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 difficult task which the natural historian has to accomplish; since on it depends the acknowledgment of the specific identity of one object 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 publication 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, believe that there exists a growing tendency, especially in some portions of the Continent, to regard every difference (if at all perma- B2 4 nent) as a specific one; and hence I gather the informa- tion that areviewal of our first principles is occasionally necessary, if we would not restrict (however gradual and imperceptibly) that legitimate freedom which Nature has had chalked out for her to sport in, or strive to im- pose laws of limitation in one department which we do not admit to be coercive in another. Perhaps, however, before entering on the subject- matter of this treatise, my definition of the terms “species” and “variety,’—so far at least as such is 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 from a common parent can alone convey: whilst the latter should be restricted, unless I am mistaken, to 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 will be perceived, takes for granted the acceptance of a dogma which I am fully aware is open to much controversy and doubt, —namely, that of “specific centres of creation.” 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 5 as involving an absurdity (which I believe to be the exact opposite of the truth), I would, in the present state of our knowledge, desire rather to regard it as a postulate, assumed to illustrate the doctrine of species, than as a problem capable of satisfactory demonstration. The second of the above definitions may likewise require briefly commenting upon ; for I have frequently 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 “ variety,” to be technically such, must have in it the primd-facie elements of stability,—and to an extent moreover that, without the intermediate links (which, although rarer than the variety itself, must nevertheless exist) to connect it with its parent stock, its condition is such that it might be registered as speci- 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, sometimes into almost white. It also most frequently happens, in such instances, that the extreme aberration is of more common 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 bemg 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 6 variety, every separate degree of colour which could possibly be found between the outer limits,—seeing that (increasing, as they did, in 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,—in- 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 differences 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 believe that it would be proper to do so: nevertheless there are instances, the results, for example, of isolation, in which adrupt modifications may be @ 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 kmdred questions, must be deferred to a subse- quent chapter of this work. CHAPTER II. FACT OF VARIATION, Ir is scarcely possible to survey the members of the external world around us without being struck with 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 mits 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 which is perpetually going on amongst created things mar their boasted constancy. The fact of aberration, to which we would briefly allude 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 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, as unmistakeably such: and in these cases, a well-edu- cated eye, although of course occasionally deceived, will not often be found to err. 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- tain 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, and to each an amount of disturbing influence (more or less, as the case may be) has been conceded. “ The 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 all work in concert to bring about that change absolutely indis- pensable to the existence of animal and vegetable life upon the earth’s surface, and that variety of conditions by which is ensured a fitting abode for each kind of its multifarious and diversified inhabitants.” Whilst exploring the barren moor, or bleak upland 9 heights, the 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 & priori antici- pated between the hard, sturdy mountaineer 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- tent; and which exhibit, when even in a state of nature, nearly as great a variety, from purely natural causes, as 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 Mammalia, BS 10 why, we may ask, are the lower members of the animal creation to be denied analogous effects from the same causes ? We are often told that the Annulosa present so many anomalies in their organization, that we cannot apply the argument of analogy, when reasoning on their 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 regards the senses of insects, which must ever remain a subject of obscurity), I contend that to accept it in all its fullness would be in the highest degree unphiloso- phical; whilst, to endorse it to the extent which even its partial advocates do imsist 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. “ Creation,” says one of our most intelligent writers of modern times, “is full of analogies, pomting to one general originator, and linking all sentient things into 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. They may often fail to produce them, and the il 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, because those “counter influences” prevail,—aud because different effects 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 innumerable; so that it is only on a broad scale that parallel results can be looked for im 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 phenomena are displayed under circumstances seemingly coincident, our first object should be (not to regard the phenomena as indicative, that no constant result can be anticipated from causes which are similar, but), to inquire whether the circumstances in question are really coincident or not,—seeing that some counter- acting stimulus may have been, here or there, 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 12 effects being observed (amongst the members of the 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 corresponding modus operandi in the maturation of like results), from a mere @ priori belief that the lower animals cannot be acted upon, by external influences, in 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- ciate and neutralize the effect of extraneous disturbing causes. Thus furnished, he will be prepared to seize on any of those minute indications which often connect phenomena which seem quite remote from each other. He will have his eyes as it were opened, that they may be struck at once with any occurrence which, according to received theories, ought zot to happen ; for these are the facts which serve as clews to new discoveries*.” There can be no doubt that amongst alarge proportion of our naturalists, differences, as such, are too exclusively studied. Essential 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. 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 interpretation of the phenomena 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 explaming 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 sciences*.” * “Magna enim hucusque atque adeo curiosa fuit hominum in- dustria, in notanda rerum varietate, atque explicandis accuratis animalium, herbarum, et fossilium differentiis; quarum plereeque Magis sunt lusus nature, quam serie alicujus utilitatis versus 14 I believe that, if analogies were more carefully studied in the lower departments of the 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 accepted by the students of the Vertebrata, our so-called “ species ” will have to submit to a process of elimination and inquiry, which at present would be well nigh incre- dible. The time for such a step is yet far off: perhaps indeed, considering the innovations of nomenclature which it would necessitate, it will never arrive at all; yet the fact remains the same, that, if analogy with creatures of a more perfect development be not altogether disallowed us, during our researches into the insect tribes, or 7f 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 rerum similitudines et analoga, tam in integralibus, quam partibus : illa enim sunt, que naturam uniunt, et constituere scientias incipiunt.”—Novum Organum, lib. ii. 27. 15 animate world, an enlargement of our prescribed limits, for specific variation, ought in reality to follow (sooner or later) as an inevitable consequence. In whichever light, therefore, insect aberration is viewed by us,—whether as a matter of experience (which, being self-evident, will satisfy the practical observer), or as probable from analogy (which will hardly be denied, at any rate to a certain extent, by even the most theo- retical), we affirm that it does, ipso facto, evist. “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. 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 “ varieties,’— 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 differ, 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 16 generally, as commonly understood) that any such 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 still, 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 analogy, and which our understanding, as it becomes gradually brighter, no less assuredly condemns. True it is, that we may not be able, as in the higher animals, 17 to appreciate the differences between individuals 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 peculiarities do unquestionably 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, of all the wondrous details which it includes, can be distinguished, except perchance the outline of its jagged peaks projected in faint relief 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 minutiz of each of its com- 18 ponent parts. And so it is with the objects which we have been just discussing. When contemplated in a mass, and by an uneducated eye, hosts of them may appear to be identical; but as our vision becomes clearer and more acute, differences, formerly inappreciable, are gradually made manifest,—until at last we can detect modifications innumerable, throughout the entire length of the living panorama; and are enabled to endorse the belief (repugnant &@ priori though it be), that individual variations, even to the extent which I have ventured to suggest, are not incompatible with specific similitudes. 19 CHAPTER III. CAUSES OF VARIATION. “Tr is not impossible,” says a writer of the 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 have 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 us not suppose that this is a mere wanton specula- 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 various modifying influences which our understanding tells us do everywhere exist. To investigate the causes of things, and to endeavour to trace out by slow, inductive processes those second- ary agents, by the assistance of which a large propor- tion of the phenomena around us are gradually matured, is no insignificant task; yet how much animadversion from without have the students in such fields of research frequently to endure! few. It is im 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- nate), and cannot be wiped out. To suppose @ 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 167 array, which the naturalist, above all others, delights to contemplate. If things are no longer to be regarded as dissimilar because they unite on their outer limits, differences may be given up, as having no special 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 (and, moreover, without injuring its individual reality) is blended into that to which it is the most akin. Night is distinct from day; yet, so long as the twilight iater- 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 amalgamate, in a central temperature. And thus it is with things material. The sea and the land are essen- tially unlike ; yet the precise boundary between the two .is never clearly defined,—the ebb and flow are constantly going on, and the line of separation is variable. The mountain-range is moulded on a different type to the level country beneath it ; yet the turning-point of them both is, in all instances, on neutral ground. We need not however adduce further evidence in support of this fact,—that, throughout the whole of Nature, the general principle of fusion (either absolute or apparent) is most obvious. From first to last, traces of it are everywhere 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 168 they are specifically dissimilar, it can only arise from their near resemblance to each other, and not from their positive coalescence. But, admitting that this universal blending, throughout the animate world, does not inter- fere with the gradual conformation of its several groups, which therefore should be recognized; we may perhaps be told by the believers in the ‘ Méthode Mononomique,’ that they do not intend to ignore the arrangement which Nature has so broadly laid down, but that, on the contrary, they tacitly endorse it,—their device having reference to the names only. To this however it will be sufficient to reply, that, if they deem it necessary (of which I am by no means convinced) to accept the natural genera of the organic creation at all, why not acknowledge them? and how can they be so well acknowledged, either in principle or practice, as through the medium of a binomial nomenclature? Such a system is the only consistent one, on the hypothesis that they do consider them of primary importance; it is more in unison with our notions of what ought to be; more suggestive of what actually is; more honest and generous to those who have laboured (as describers), with such care and diligence, before us. It will be perceived, from the above remarks, that, although professedly criticizing the ‘Méthode Mono- nomique,’ into the analysis of which my subject has unintentionally drawn me, it is the absurdity of ob- jecting to genera because they are not rigidly defined throughout, that I have been mainly striving to con- 169 demn. It is indeed well nigh incredible that any such strictures could ever have been advanced; for it must surely have occurred to the most superficial inquirer, that genera, after all, cannot be homogeneous,—seeing that they are necessarily composed of detached species, no two of which are precisely similar, even in the few structural details which may have been accidentally chosen for generic diagnostics. How is it possible, therefore, that mere groups, even though they be in accordance with Nature, should be so far isolated and uniform in their character as to occupy an analogous position to that of the absolutely independent species (of distinct origins) which they severally contain ? Taking the preceding considerations into account, the question will perhaps arise,—How then is a genus to be defined? To which I may reply that, were I asked whether genera had any real existence in the animate world, my answer would be that they undoubtedly have, —though not in the sense (which is so commonly supposed) of abrupt and disconnected groups. I con- ceive them to be gradually formed nuclei, through the | gathering together of creatures which more or less resemble each other, around a central type: they are the dilatations (to use our late simile) along a chain which is itself composed of separate, though differently shaped links,—the links being the actual species them- selves, and the swellings, or nodes, the slowly developed genera into which they naturally fall. When I say I 170 “slowly developed,” my meaning may possibly require some slight comment. It is simply therefore to guard against the fallacy, which I have so often disclaimed, that genera are abruptly (or suddenly) termimated on their outer limits, that the expression has been employed. Though I believe that a series of species, each partially imitating the next in contact with it, is Nature’s truest system; yet we must be all of us aware that those species do certainly tend, in the main, to map out assemblages of divers phases and magnitudes, distin- guished by peculiar characteristics which the several members of each squadron have more or less in common. So that it is only in the middle points that these various groups, respectively, attain their maximum,—every one of which (by way of illustration) may be described as a concentric bulb, which becomes denser, as it were, in its successive component layers, and more typical, as it approaches its core. If, then, the theory of genera be such as I have endea- voured to expound, it results from what has been said, that every generic type ts to be looked for in, or about, the centre of its peculiar group,—oy at any rate in that region of it which would seem to be the most charac- teristically, or evenly, pronounced. I lay particular stress upon this conclusion, because (if correct) it will somewhat modify the notions which are occasionally entertained upon the subject. A stricture, however, may here be required upon what I have advanced, lest, 171 through using the metaphors which I selected for the elucidation of a principle, it be supposed that I would wish them to apply to the smaller details, likewise, of the problem. If a genus has been portrayed under the similitude of a bulb, or of a nodule (formed by the ap- proximation of beads which more or less resemble each other in their primary aspect), it does not follow that’ either bulb or nodule are to diminish in a similar ratio towards their respective circumferences,—or, which is the ° same thing, that they are to be symmetrical ; whether spherical, ovoid, or otherwise. The general method of the organic creation is a progressive one; and its suc- cessive types, therefore, will not always be found to radiate equally from their normal foci: so that itis in the direction of the higher (rather than the lower) extre- mities of the assemblages that those foci are usually to be discerned ;—and where the groups are large, it is not often difficult to pronounce which of their ends are, as a whole, the more perfectly developed. Tt will, moreover, be further acknowledged (Gf my premises are allowed), that, since it is a somewhat central position which the typical member of a genus usually occupies, the diagnostic characters, although (in combination) carried out to the full, are more evenly balanced in a generic type than in any of its associates ; or, in other words, that a species in which any single organ is monstrously enlarged, at the expense of the rest, is seldom typical of the assemblage with which it is placed ; but may be @ priori regarded as in all proba- a 172 bility a transition form, leading us onwards into some neighbouring group*. I will not, however, venture too closely into this ques- tion in its minor bearings ;—suffice it to have demon- strated that, whatever be the rate, law, or direction, of the advancement of the various groups towards a more perfect model ; or in whatsoever position the several types are to be discerned, with respect to their immediate associates, genera cannot be isolated and distinct, but must of necessity merge (each into two or more others) on their outer limits. Hence, if such be the case, as I contend that it usually is (the exceptions to the rule being, as I shall hope shortly to prove, the result of accident, and by no means a part of the original design), it may perhaps be a problem, how far we are justified in rejecting many large and natural assemblages, through the fact that they blend, both at their commencement and termination, imperceptibly, 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 many extensive departments they combine with each other so completely at their extremities (although sufficiently well-marked in the mass), that, unless we are prepared * J may add, that this suggestion, as to the evenly balanced state of 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. 1738 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 grades brought to light: so that their apparent isolation may oftentimes arise from our ignorance of the absent links, rather than from the fact itself. It would surely be more desirable, therefore, when viewed even in the light of expediency alone, to submit to the possi. bility of a few neutral species being conceded, with equal reason, to different groups, than to amalgamate the whole, and so lose sight of the general method or arrangement, into which the various creatures do un- questionably (in a broad sense) dispose themselves. If, however, there be any truth in the generic doctrine as above enunciated, the question of convenience may be omitted from our speculations in t¢oto,—seeing that all genera (except those whose present abruptness is the effect of accident) fuse into others with which they are in immediate contact: so that in reality, unless we ignore these natural assemblages from first to last, we have no choice left us 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 in one or the other of two consecutive groups,—according 174 to the judgment of the particular naturalist who has to deal with them. But let us glance at the subject through the medium of an example, and endeavour to realize what would be the consequence of that wholesale combination at which we must sooner or latter arrive, if genera are not to be upheld because they slowly merge into each other as we recede from their respective types. The immense de- partment Carabide, 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 to assume modifications of form which attain their max- imum only in successive centres of radiation, must often- times be regarded as generic, if we would not shut our eyes altogether to the natural collective masses into which 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 shall 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 Linnean 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. 175 under the former contingency the determination of species would become practically well nigh hopeless, it is far from unlikely that we shall eventually hail the latter as, after all (at any rate to a certain extent), the more con- venient of the two. Look, for instance, at the great genus Pterostichus, which has nearly 200 representatives in Europe alone: true it is that its several sections (Pecilus, Argutcr, Omaseus, Corax, Steropus, Platysma, Cophosus, Pterostichus proper, Abax, Percus,and Molops), 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 that they have not been retained as separate. And this opinion may be rendered somewhat more plausible, from the knowledge that certain of the Pterostichi (the Argutors, for instance) approach so closely, in their trophi, to Calathus, as to be hardly discernible from it ; which latter genus is scarcely distinguishable (struc- turally) from Pristonychus,—a form which, in its turn, leads us on towards another type. Who would have imagined, again, some fifty years ago, that the widely distributed groups, Calosoma and Carabus, were not thoroughly detached inter se? yet what naturalist now can draw an exact line of demarcation between them ? And so it is with numerous others, which it is needless to recall. The practical inference, however, from the whole, is this: that if genera must be rejected because they are not homogeneous and isolated throughout, the 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 shall 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 their outer limits, from accident. Briefly, then, it is through the extinction of species that groups may, in 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 than mere “exceptions” (as commonly understood by that term), the result of positive disturbances from without. Yet, that genera thus distinctly bounded, at either end, do actually occur, must be self-evident to any one who has attempted to study the distribution of organic beings with reference to the geological changes which have taken place on the earth’s surface ; for it is clear that a vast proportion of the creatures which inhabit our globe came into existence at periods anterior to many of those great convulsions which altered finally 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 177 more than a fancy or romance, it is certain that nume- rous members of many geographical assemblages must have perished for ever during the gigantic sinkings which have at various epochs been brought about. From which it follows, that those groups, or clusters, of which but few representatives (comparatively) are extant, will 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 reduced. Although there are many means through which species may become annihilated, yet, since the sub- sidence of a tract into the sea involves the maximum of loss which a space of that magnitude can sustain, the above conclusion gives rise to a corollary: that it is in islands that we should mainly look for genera which are to be rigidly pronounced. The question therefore naturally suggests itself,—Is this in harmony with what we see; or, in other words, is it consistent with ex- perience, or not? I believe that it is; for I think it will be found, on inquiry, that the greater proportion of those groups which are more especially isolated in their character (I do not say, necessarily, the most anomalous ; though this in some measure follows from the fact of their detachment) are peculiar to countries which are 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 15 178 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 akin, and that where the creatures which unite in composing it are of slow diffusive 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 he 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 (‘ Zoologist,’ 2344) ; and it still swarms on asmall rock off Lundy Island, in the Bristol Channel. It is reported, moreover, to have been lately re-introduced at Liverpool. 179 whelming effect of a volcanic eruption, in a region where the aborigines of the soil have not wandered far from their primeval haunts, may, as Sir Charles Lyell has well remarked, put an end to others, and so effect the separation of their allies from the central stock. 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 or chance; and we must not deduce our ideas of genera from the examples which ¢hey supply. We should rather reflect, that it is no matter of mere speculation, that many organic links, now absent, have, through the crises and occurrences to which we have just drawn attention, become lost. On the contrary, indeed, we know that, in the common course of things, it must have been so; and therefore we are induced to regard those cases as exceptional, and as in no way expository of Nature’s universal scheme. The more we look into the question, whether by the light of analogy or the evidence of facts, the more are we convinced that lmes of rigid demarcation (either between genera or species, though especially the former) do not anywhere, except through accident, exist. And hence it is that we ascend, by degrees, to a comprehension of that unity at which I 180 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. 181 CHAPTER VII. Deposita sarcina, levior volabo ad coelum.—S. Jerome. Havine now completed the short task which I had undertaken to perform, I will, in conclusion, offer 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. Commencing with the thesis, that specific variation, whether as a 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, in the 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 182 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 adso- lute uncertainty than to follow such a guide; unless it be reasonable to put out our candle because we have not the light of the sun, it must be reasonable to direct our steps by probability, when we have nothing clearer to walk by *”’. 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 everywhere abound: and, thereupon, to pro- voke the inquiry, whether entomologists, as a mass, have usually taken them into sufficient account, when de- scribing as “species,” from distant quarters of the globe, insects which recede in only minute particulars * Religion of Nature Delineated, p. 103. 183 from their ordinary states. My own impression is, that 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 subject is fairly looked into and analysed, it is impossible not to be convinced, that the primd-facie aspect of these creatures is eminently beneath the control of the several conditions to which they have been long exposed. But let me not be misunderstood in the conclusion which I have been thus compelled to endorse, or be supposed to ignore the fact that truly representative species may frequently occur in countries far removed from each other; which cannot therefore be regarded as modifica- tions of a common type. I believe, 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 is) for the multiplication of our, so called, “ specific novelties.” I suspect, indeed, that actual representative species (if they may be thus expressed) are more often 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 detected in opposite divisions of the earth, it is more often the case that members of them have been trans- ported at a remote period (either by natural or artificial means) from their primeval haunts, and have become gradually altered by the circumstances amongst which 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 a real existence in Nature’s scheme; and 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 connected by an 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 “species”? are traceable in countries which geology demonstrates to have been far asunder during the entire interval since the first appearance of the present animals and plants upon our earth, there is at any rate an @ 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 185 have been usually considered to be “ representative” ones, were members, in the first instance, of the self- same assemblages,—which had wandered to a distance from their primeval haunts, and were afterwards, through the submergence of the intervening land, cut off from their allies. I have adduced, in a preceding chapter, some remarkable examples in illustration of this hypothesis,—an hypothesis which I believe to be the true clue to a very large item of the “ specific representation ”’ theory. A considerable number of the Madeiran Helices may be cited (which I have already done*) as, in the strictest sense, representative of each other,—and as therefore specifically distinct: and I may add, that it is to island groups that we must mainly look for this system in its full development. But, apart from the fact that I would not wish to 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 what 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 the action of local influences on the members of the insect world. It has been my aim, in the preceding pages, to call attention to the importance of external circumstances and conditions in regulating, within defi- nite limits, the outward aspect of the Articulate tribes. * Vide supra, p. 128. 186 I do not, however, assert that every species is liable to be interfered with ad 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 mischievous of dogmas, that they are ail-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 @ moment maintained, so long as facts (and not reason- ing only) are to be the basis of our speculations. I repeat, that it is merely 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 minutize and detail, should ever have upheld so monstrous a doctrine as that of the transmis- sion of one species into another,—a doctrine, however, 187 which arises almost spontaneously,—if we are to assume that there exists in every race the tendency to an un- limited progressive improvement. There are certainly no observations on record which would, in the smallest degree, countenance such an hypothesis. Many animals and plants, it is true, are capable of considerable modifi- cations and changes, for the better,—very much more than is the case with others. But what does this prove, except that their capacity for advancement has a slightly wider compass than that of their allies? It touches not the fact, that the boundaries of their respective ranges are absolutely and critically defined. It is moreover a singular phenomenon, and one in which the strongest proofs of design (or a primary adjustment of limits with a view to the future) may be discerned, that the mem- bers of the organic creation which display the greatest adaptive powers, are those which were apparently des- tined to become 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 plants. It usually happens that those species which have the greatest pliability of organiza- tion, those which are most capable of accommodating themselves to a great variety of new circumstances, are most serviceable to man. These only can be carried by him into different climates, and can have their pro- perties or instincts variously diversified by differences of nourishment and habits. If the resources of a species 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 utility. We may consider, therefore, that in the domestication of animals and the cultivation of plants, mankind have first selected those species which have the most flexible frames and constitutions, and have then been engaged for ages in conducting a series of experiments, with much patience and at great cost, to ascertam 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 stance, 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 the same? Look, for example, at the Tarphii (to which I have already alludedt+) of Madeira: I have detected about eighteen abundantly defined species; and, as stated in a previous chapter, I have but little doubt, from their sedentary habits, and the evident manner in * Principles of Geology, 9th edition, pp. 583, 584. + Vide supra, p. 121. 189 which they are adjusted to the peculiarities of the region in which they obtain, that they are strictly an esoteric assemblage, inhabiting the actual sites (or nearly so) of their original début upon this earth. Here, then, we have a sufficient length of time for developments to have 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 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- plained on the doctrine of transmutation : yet they are no exceptions to the ordinary rule,—occupying an ana- logous 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 shown that, in thus con- ceding a legitimate power of self-adaptation, in accord- ance with external circumstances, to the members of 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 190 have often, because permanent, been at once regarded as specific, may not be sometimes rendered intelligible by a knowledge of the localities in which the creatures have been matured), I do not necessarily open the door to the disciples of Lamarck, or infringe upon the strict orthodoxy of our zoological creed. On the contrary, indeed, I believe that the actual reverse is nearer the truth ; and, moreover, that those very hyper-accurate definers who recognize a “species”? wheresoever the minutest decrepancy is shadowed forth, will be found eventually (however unaware of it themselves) to have been the most determined abettors of that dogma,—see- ing that their species, if such they be, do most assuredly pass into each other. We must not, however, omit to notice, briefly, how this perversion of Nature’s economy took its rise. It was from the desire, which is almost inherent within us, to account for everything by physical laws; and to dis- pense with that constant intervention of the direct crea- tive act which the successive races of animals and plants, such as are proved by geology to have made their appear- ance at distinct epochs upon this earth, would seem to require. Or, which amounts to the same thing, it resulted through an endeavour to explain by material processes what is placed beyond their reach. But, if this be the case, it may be reasonably asked,—Are mate- rial laws then not to be inquired into, and should the various influences which operate in the organic world around us be debarred from analysis? Unquestion- 191 ably not. Truth is truth, under whatever aspect it may come; and cannot possibly contradict another truth. To exercise our intellectual faculties, by tracing out, through slow, inductive methods, the modus operandi of 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 conceit that our own imperfect interpretations have left nothing more to be found out, that the great danger is 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 something ; but it does not necessarily follow that we have done much. On the contrary, it often happens that, in so doing, we have achieved wonderfully little,—seeing that the pro- blem may be self-evident. Behind that “cause,” we should recollect, 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 Final One,—with which alone the mind can be thoroughly content. “ We make dis- covery after discovery,” says Dr. Whewell, “in the various regions of science; each, it may be, satisfactory, and in itself complete, but none final. Something 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 192 sweet, full and harmonious; but never reaches a close: no cadence is heard with which the intellectual ear can feel satisfied*.”’ As regards that most obscure of questions, what the limits of species really are, observation alone can decide the point. It frequently happens indeed that even observation itself is insufficient to render the lines of demarcation intelligible,—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, 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 centuries, have become modified by man,—the starting- 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. 193 trolled, are by constitution more tractile (and possess, therefore, more decided powers for aberration) than the rest. Whether traces of design may be recognized in this circumstance, or whether those forms were originally selected by man on account of their pliability, it is not for me to conjecture ; nevertheless, the first of these in- ferences is the one which I should, myself, be @ priori inclined to subscribe to. In examining, however, this enigma, of the 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- larly flexible organization present, should not unneces- sarily predispose us to dispute the question in its larger and more general bearings. Nor should we be unmind- ful that (as Sir Charles Lyell has aptly suggested) “some mere varieties present greater differences, inter se, than do many individuals of distinct species ;”’ for it is a truth of considerable importance, and one which may help us out of many an apparent dilemma. But, whatever be the several ranges within which the members of the organic creation are free to vary; we are positively certain that, unless the definition of a species, as involving relationship, be more than a delusion or ro- mance, their circumferences are of necessity real, and must be indicated somewhere,—as strictly, moreover, and rigidly, as it is possible for anything in Nature to be K 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,— ** Still changing, yet unchanged ; still doom’d to feel Endless mutation, in perpetual rest.” INDEX. Aberration, perhaps indicated universally, 16, 17, 18. Aborigines, insect, unimportant for climatal modifications, 25, 26, 27. Aealles, the Canarian type of, apparent on the Salvages and De- zertas, 124, Neptunus, Woll., perhaps a state of A. argillosus, 124. Achatina Eulima, Lowe, its extinction in Porto Santo, 131. Achenium Hartungii, Heer, a form of A. depressum, 65. Acherontia Atropos, Linn., its introduction into Madeira perhaps recent, 74. Adimonia, the capture of, out at sea, 150. Aépus marinus, Strom., pallid hue of, 64. Robini, Lab., pallid hue of, 64. Agabus bipustulatus, Linn., unaffected by climate, 31. Alligators, their peculiarity to 8. America, 143. Alpine species, some peculiarly so, 40. Altitude and latitude, sometimes reciprocal, 35, 114. Amycterus, its concentration in Australia, 143. Amyot, M., his ‘Méthode Mononomique,’ 164. Analogies, Lord Bacon on the importance of, 13; why necessary to be studied, 14. Analogy, argument from, 10, 11, 12. Anchomenus marginatus, Linn., slightly modified in Madeira, 38. Andes, dissimilarity of the fauna on the opposite sides of the, 146. Anobium striatum, Oliv., unaffected by climate, 31. Antenne, joints of, said occasionally to vary, 96. Anthicus bimaculatus, Mllig., variability of, near the sea, 63. —— fenestratus, Schmidt, slightly modified in Madeira, 38. —— humilis, Germ., variability of, in salt places, 63. —— instabilis, Hoffm., pallid hue of, 64. Anthonomus ater, Mshm, very small in Lundy Island, 58, 73. Aphelocheirus estivalis, Fabr., the hemelytra of, sometimes fully developed, 100. Aphodius nitidulus, Faby., paler in Madeira than in Europe gene- rally, 65. K 2 196 INDEX. Aphodius plagiatus, Linn., usually black in England, 61; two distinct states of, indicated, 105. Apocyrtus, 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 5. America, 143. Armitage, Mr.,on Cicindela fasciatopunctatafrom Mount Olympus,4}. 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 Laparocerus, 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 difference between primary and recent, 145 ; their hindrance to insect diffusion, 145. Bembidium Atlanticum, Woll., paler in Porto Santo than in Ma- deira, 66 ; the variations to which it is subject, 107, 108. bistriatum, Dufts., paler in saline districts, 62. ephippium, Mshm, pallid hue of, 64. obtusum, Sturm, varies in southern latitudes, 33. pallidipenne, Nig., pallid hue of, 64. saxatile, Gyll., variety of, on the south coast of England, 60. Schmidtti, Woll., perbaps a state of B. callosum, 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. Boromorphus, common to Madeira and Sicily, 139. Brachinus crepitans, Linn., two distinct sizes of, frequently indi- eated, 105. Bradycellus fuluus, 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 Pristonychus, 175. complanatus, Koll., varies from altitude, 39; variety of, on one of the Madeira Islands, 88. fuscus, Fabr., slightly modified in Madeira, 38, 85. INDEX. 197 al melanocephalus, Linn., smallness of, in the Scilly Islands, 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, merges gradually into Carabus, 175. Syncophanta, Linn., its power of crossing the sea, 147. Canary Islands, migratory direction of their insect population, 119. Carabide, inconstant in their organs of flight, 43; family of, nearly similar throughout in its oral organs, 174. Carpophilus hemipterus, Linn., unaffected by climate, 31. Caulotrupis conicollis, Woll., large size of, on one of the Madeira Islands, 88, 109. lucifugus, Woll., varies from isolation, 90, 109. Causes, never final ones which we investigate, 191. Centrinus, its concentration in 8, America, 143. Ceutorhynchus contractus, Mshm, smallness of, in Lundy Island, 59, 73. Cholovocera, common to Madeira and Sicily, 139. Choreius ineptus, Westw., on a winged state of, 44. Chorosoma miriforme, the development of the wings of, 100. Chrysomela, apterous in Madeira, 82. Chrysomele, vary from altitude, 41. Chrysomelide, almost absent in Tierra del Fuego, 47. Cicindela fasciatopunctata, Germ., a state of C. sylvatica, 41. Cicindelide, often variable, 41. Cillenum laterale, Sam., lurid hue of, 64. Cimex apterus, Linn., the development of the wings of, 100. lectularius, Linn., on the development of the wings of, 45. Cistela sulphurea, Linn., its variability near the sea, 60. Clausilia deltostoma, Lowe, a Porto-Santan form of, 134. Climatal modifications significant, although small, 42. Climate, not important as a disturbing cause, 23, 24, 31, 32, 42. Clouded-yellow Butterfly, unaffected by climate, 31. Clypeaster pusillus, Gyll., differs slightly in Madeira, 65. Coast, inconstancy of-insects in the vicinity of the, 57. Coccinella 7-punctata, Linn., unaffected by climate, 31. Colias Edusa, Fabr., unaffected by climate, 31. Colour, its inconstancy in insects found near the sea, 57, 58. —— of insects, affected by isolation, 88. Colymbetes, a species of, captured forty-five miles from shore, 149,150. Compensation, generally apparent when an insect is deprived of an organ or sense, 81 Coranus subapterus, Curt., the development of the wings of, 101. Cordillera, Mr. Darwin on the fauna of the, 145. 198 INDEX. Corylophus, apterous in Madeira, 82. Criomorphus, Curtis, referable to the genus Delphaz, 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 8. 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 sawatile, 60. Definition of the term ‘ species,’ 4; of the term ‘ variety,’ 4. Delphax, on the development of the wings of, 45, Dermestes vulpinus, Fabr., unaffected by climate, 31. Deucalion, its oceurrence on the Salvages and Dezertas, 125. Desertarum, Woll., its sedentary nature, 125, 126, 127. Dichelus, its concentration in 8. 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. obscuroguttatus, 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. Ellipsodes 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 applicable, 118. Entomology, the study of, does not necessarily cramp the mind, 111. Ephistemus, apterous in Madeira, 82. Eucalypti, their concentration in Australia, 142. Eunectes sticticus, Linn., unaffected by climate, 31. Euphorbias, their concentration in Southern Africa, 142. INDEX. 199 Eurygnathus Latreillei, Lap., variety of, on one of the Madeira Islands, 88, 109. Exceptions, not be allowed to negative a law, 72, 73. Extinction of species, as indicated in the Madeiran Helices, 131 ; the only cause by which genera may be abruptly defined, 176. 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, 137. Forests, the hindrance which they offer to insect-diffusion, 154. " nae Islands”’ of the ancients, probably the Canarian group, Galapagos, fauna of, 23. Genera, the nature of, often misunderstood, 160; a familiar expla- nation of, 160, 161, 162; cannot be abrupt except trom accident, 169; how to be defined, 169; the types of, usually situated towards the centres of the several groups, 170; the types of, usually evenly balanced in their structural characters, 171, 172; may be abruptly defined from accidental causes, 176, 177. Generic areas, an important feature throughout Nature, 130,141, 184. Geology, a necessary item in the study of insect-diffusion, 113. Germanic plains, the, probably a primary area of diffusion, 130. Gerris, on the development of the wings of, 100. Gould, Mr., on the Swallows of Malta, 102. Gymnaétron, blood-red dashes characteristic of, 62. Campanule, Linn., its smallness on the Cornish coast, 58. Veronice, Germ., a variety of G. niger, 62. Hadrus illotus, Woll., perhaps a form of H. cinerascens, 66. Haliplus obliquus, Gyll., dark state of, in Ireland, 67. Haltica exoleta, Fabr., its variability on the coast, 59. Harcourt, Mr., on the discovery of Madeira, 49, 50. Harpalus vividus, Dej., changes to which it is subject, 67, 68, 69; variable in the connateness of its elytra, 96, 97. Hegeter, its maximum attained in the Canaries, 120. elongatus, Oliv., its migration from the Canaries, 120; of a more adaptive nature than its allies, 121. latebricola, Woll., its occurrence in the Salvages, 120. Helices, have often two distinct states, 106; many of them repre- sentative in the Madeira Islands, 128, 129; those in the Madeiras chiefly of slow migratory powers, 130, 131. Helix attrita, Lowe, its local character, 132. Bowdichiana, Fér., perhaps a gigantic state of H. punctulata, 106. — calculus, Lowe, sedentary nature of, 132. 200 INDEX. Helix commixta, Lowe, sedentary nature of, 132. coronata, Desh., its peculiarity to Porto Santo, 128; its occur- rence beneath the surface of the ground, 131. coronula, Lowe, its peculiarity to the Southern Dezerta, 128. Delphinula, Lowe, the Madeiran representative of H. tectifor- mis in Porto Santo, i129. discina, Lowe, a form of H. polymorpha, 133. erubescens, Lowe, its powers of diffusion greater than those of its allies, 183; sensitive to external influences, ] 34. fluctuosa, 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, 134. Lowei, Pfr., perhaps a gigantic state of H. Portosanctana, 106. papiho, Lowe, a form of H. polymorpha, 133. paupercula, Lowe, its powers of diffusion greater than those of its allies, 133. polymorpha, Lowe, sensitive to external influences, and of great diffusive powers, 133. Portosanctana, Sow., its peculiarity to Porto Santo, 129. pulvinata, Lowe, 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. —— Vuleanus, 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 of Phosphuga atrata, 102. Holoparamecus, common to Madeira and Sicily, 139. —— niger, Aubé, different in Madeira and Sicily, 33. INDEX. 201 Hooker, Dr., on the insects of Kerguelen’s Land, 86. Humboldt, his notice of Sphinxes and flies high up on the Andes, 149. Mumpting- Buda their peculiarity to S. America and the W. Indies, Hydrobius, apterous in Madeira, 82; the capture of, out at sea, 150. Hydrometride, on the development of the wings of, 100. Hydroporus, the capture of, out at sea, 150. confluens, Fabr., unaffected by climate, 31. Hypsonotus, its concentration in S. America, 143. Influence of climate not important, 23. Insect-aberration, perhaps a universal fact, 16, 17, 18. Insule Fortunate of Juba, probably the Canarian Group, 141. Ireland, poverty of the fauna of, 52, 53; the south-west of, has something in common with Madeira, 139. Islands, faunas of, often too greatly magnified, 70; the species of, generally more isolated in their structure than those of continents, Isolation, effects of, on insect-stature, 71. Txias, their concentration in Southern Africa, 142. Kangaroos, their concentration in Australia, 142. Kerguelen’s Land, insects of, 86. Kirby, Rev. W., on insects washed up on the Suffolk coast, 147. Lemophieus pusillus, Schonh., unaffected by climate, 31. Lamprias chlorocephalus, Ent. H., two distinct sizes of, frequently indicated, 105. Laparocerus morio, Schonh., large size of, on one of the Madeira Islands, 88. Latitude and altitude, sometimes reciprocal, 35. Leistus montanus, Steph., has been supposed to be equal to L. fulvi- barbis, 40. Lemur, its peculiarity to Madagascar, 143. Litargus, common to Madeira and Sicily, 139. Lixus angustatus, Fabr., unaffected by climate, 31. Localities, some naturally more productive than others, 53, 54, Longitarsus, the native species of, apterous in Madeira, 82. Loricera, apterous in Madeira, 82. Lowe, Rev. R. T., his capture of Deucalion Desertarum, 127. Lundy Island, smallness of the insects in, 58, 59; occurrence of the Black Rat in, 178. Lycena Phieas, Linn., darker in Madeira than in England, 34. Lyell, Sir Charles, on Helix hirsuta, 106; on the fossil period of the Madeiran Helices, 129; on insects washed up on the shore, 148; on the effect of gales in the transportation of insects, 148 ; 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. Lygeus brevipennis, Latr., on the development of the wings of, 101. 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 msect 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. brevicollis, 66. Man, agency of, in the destruction of species, 179. Mantura Chrysanthemi, Ent. H., variability of, in Lundy Island, 59. Marsupialia, their concentration in Australia, 142. Mesembryanthemums, their concentration in Southern Africa, 142. Mesites, a modification of Cossonus, 144. Maderensis, Woll., its near relationship to the M. Tardii, 141. Tardii, Curtis, its variability near the coast, 58. ‘Méthode 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 Australia, 142. Mollusca, Terrestrial, often present two distinct states, 106. Moluris, its concentration in 8. Africa, 143. Monochelus, its concentration in 8. Africa, 143. Mountain-chains, their hindrance to insect-diffusion, 145. Mouxitain-tops, either very prolific in insect life, or else barren, 115. Mus Rattus, almost exterminated in England, 178. Mycetoporus pronus, Erichs., two distinct states of, indicated, 106. Myrtles, their concentration in Australia, 142. Naturalist, the, what his province to investigate, 158. Nature, not irregular because presenting occasional anomalies, 94. Naupactus, its concentration in 8. America, 143. Nebria complanata, Linn., unusually pale near Bordeaux, 33 ; pallid hue of, 64. Ne ioe some of its insects perhaps but states of those of the 1d, 37. Nomenclature, a binomial system the only true one, 164, 168. Notuphus, the capture of, out at sea, 150. Notiophili, extremely variable, 40. INDEX. 203 Notiophilus geminatus, 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, 145. Ochthebius marinus, Payk., lurid hue of, 64. Olisthopus, apterous in Madeira, 82. os Mi gerentes, Woll., large state of, on one of the Madeira Islands, » 89. rotundatus, Payk., very small in the Scilly Islands, 58, 73; subapterous in the Scilly Islands, 102. Omaseus nigerrimus, Dej., a form of O. aterrimus, 33. Omias Waterhousei, Woll., large state of, on one of the Madeira Islands, 88, 109. Oncocephalus griseus, development of the wings of, 101. Othius, apterous in Madeira, 82. Ourangs, their peculiarity to the Indian Islands, 143. Oxyomus, a modification of Aphodius, 144. Pachymerus brevipennis, the development of the wings of, 100. Pachyrhynchus, its concentration in the Philippine Islands, 143. Painted-Lady Butterfly, unaffected by climate, 32. Papilio Machaon, Linn., unaffected by climate, 31. Paropsis, its concentration in Australia, 143. Patagonia, insects of, distinct from those of Tierra del Fuego, 47, 48. Patrobus septentrionis, Dej., has been supposed to be a state of P. excavatus, 40. Pecteropus, its maximum attained in the Canaries, 124. Maderensis, Woll., varies from altitude, 39. rostratus, Woll., varies from isolation, 90. Pelargoniums, their concentration in Southern Africa, 142. Pelophila borealis, Payk., larger in Ireland than in the Orkneys, 33. Phaleria cadaverina, Fabr., pallid hue of, 64. Phithydrus melanocephalus, Oliv., two states of, frequently indicated, 105. Phicwophagus, apterous in Madeira, 82. Phosphuga atrata, Linn., taken with the wings developed, 102. —— subrotundata, Leach, the Irish form of the P. atrata, 33. Phytophaga, preponderance of, in the tropics, 28, 29. Pieris Brassice, Linn., varies in Nepaul and Japan, 34. Pissodes notatus, Fabr., unaffected by climate, 30. Platyomus, its concentration in 8. America, 143. Platyrrhini, their peculiarity to 5S. America, 143. -Pogonus luridipennis, Germ., lurid hue of, 64, Pontia Brassice, Linn., its introduction into Madeira probably re- cent, 74. 204, INDEX. Porto Santo, origin of the name of, 49; a generic area of radiation for certain Helices, 130. Predacious insects, less numerous in the tropics, 28, 29. Prostemma guttula, Fabr., the development of the wings of, 100, 101. Psylliodes, a variable species of, in Lundy Island, 60. fe, erythrocephala, Linn., two distinct states of, frequently indi- cated, 105. marcida, Mlig., pallid hue of, 64. nigricollis, Mshm, a pale state of the P. erythrocephala, 105. vehemens, Woll., varies from isolation, 90. Pterostichus, its various divisions are natural ones, 175. Ptini, their stature affected by isolation, 74; which characters of, are the most constant, 104. Ptinus albopictus, Woll., its changes on the islands of the Madeiran Group, 75—77. Pupa, often two distinct states of, 106. Purpurarie of the ancients, probably the Madeiran Group, 141. Pyrenean region, the, perhaps a primary area of diffusion, 130. Reasoning, not sufficient of itself for the formation of science, 159. Red-Admiral Butterfly, its introduction into Madeira perhaps re- cent, 74. Reduviade, on the development of the wings of a representative of the, 101. Representative species, exemplified by the Madeiran Helices, 128, 129, 185; where frequently to be recognized, 183. Rhyzopertha pusilla, Fabr., unaffected by climate, 31. Rivers, their power of transporting insects along their course, 149. Saline spots, variation of insects in, 57. Salvages, occurrence of a Canarian form on the, 120, 124. Saprinus, a modification of Hister proper, 143. nitidulus, Fabr., two distinct states of, indicated, 106. Scarabeus, the capture of, out at sea, 150. Scarites abbreviatus, Koll., large size of, on one of the Madeira Islands, 88 ; varies both from isolation and altitude, 91. Sciences, the, should assist rather than oppose each other, 155, 156. Scydmenus Helferi, Schaum, smaller in Madeira than in Sicily, 65. Scymnus, an apterous species of, in Porto Santo, 82. Sea, inconstancy of insects in the vicinity of the, 57. Sicily, the fauna of, has much im common with that of Madeira, 139. Silpha atrata, Linn., presents a distinct state in Ireland, 33. Silybum Marianum, Grtn., its stalks the food of a Ptinus, 76. Similitudes, Lord Bacon on the importance of, 13. Sitonia gressoria, Ilig., perhaps a form of the S. grisea, 33. Sitophilus granarius, Linn., unaffected by climate, 31. INDEX. 205 Sitophilus oryze, Linn., unaffected by climate, 31. Sloths, their peculiarity to S. America, 143. Species, definition of the term, 4; familiar explanation concerning the nature of, 161, 162; limitation of, how to be attempted, 192; limits of, real, though often difficult to trace out, 193; in a cer- tain sense both unstable and permanent, 194. Specific centres of creation, 5. Sphinx Convolwuli, Linn., its introduction into Madeira probably recent, 74. Swine, on one of the Reduviade, 101; on Oncocephalus griseus, Stapelias, their concentration in Southern Africa, 142. States, large and small ones indicated in some insects, 105. Stature of insects, smaller in islands than on continents, 70. Stenolophus Skrimshiranus, Steph., perhaps a state of S. Teutonus, Stenus Heeri, Woll., two distinct states of, indicated, 106. Structural characters, seldom variable in the Insecta, 95. Subsidences, the effect of, on insect life, 114. Swallow-Tail Butterfly, unaffected by climate, 31. Syncalypta, apterous mm Madeira, 82. Tachyporus nitidicollis, Steph., perhaps a state of T. obtusus, 33. Tarphii, their economy in the Madeira Group, 121. Tarphius, its maximum attained in Madeira proper, 121 ; common to Madeira and Sicily, 139. —— gibbulus, Germ., the Sicilian exponent of the genus, 123. Lowei, Woll., of a more adaptive nature than its allies, 122. Tarus, always apterous in Madeira, 82. lineatus, Schonh., assumes a distinct state in Madeira, 65. Telephorus testaceus, Linn., its variability in Lundy Island, 59. Thompson, Mr., on the reptiles of Ireland, England, and Belgium, 136. Thorictus, common to Madeira and Sicily, 139. Tierra del Fuego, insects of, 47; has many characters in common with Madeira, 48—51. Time, an important item in the question of modifications, 77. Toucans, their peculiarity to S. America and the W. Indies, 142. Transmutation-theory, unsoundness of the, 186—189 ; how it took its rise, 190. Trechus, always apterous in Madeira, 82. alticola, Woll., perhaps a state of T. custos, 39. lapidosus, Daws., pallid hue of, 64. Tree-Porcupines, their peculiarity to S. America, 143. Tribolium ferrugineum, Fabr., unaffected by climate, 31. Trogosita mauritanica, Linn., unaffected by climate, 31. 206 INDEX. Tropics, exuberance of the, 27,28; relative proportions of the insect tribes within the, 28, 29. Tychius, always apterous in Madeira, 82. Unity, indicated in the organic creation, 179, 180. Vanessa Atalanta, Linn., has a different aspect in N. America, 34; perhaps a recent introduction into Madeira, 74. Callirhoé, Fabr., smaller in Porto Santo than in Madeira, 73. Variation in the Insecta, a matter of experience, 7, 8, 15; probable from analogy, 15; perhaps indicated in every individual, 16, 17; 18; restricted, 35. Variety, definition of the term, 4. Velia, on the development of the wings of, 100. Waterhouse, Mr., his opinion concerning generic types, 172. Westwood, Mr., on Papilio Machaon from the Himalayas, 32; on American specimens of Lycena Phileas, 34; on the effect of heat in developing the wings of insects, 44; on a winged state of Choreius ineptus, 44; on the development of the wmgs in Del- phax, 45; on a winged state of Cimex lectularius, 45; on Aphelo- cheirus estivalis, 100; on the development of the wings of the Hydrometride, 100; on Cimea apterus, 100; on Prostemma gut- tula and Coranus subapterus, 101; on the development of the wings of Lyg@us brevipennis, 101. Whewell, Dr., on the natural causes which science has to investi- gate, 191. White-Cabbage Butterfly, varies in Nepaul and Japan, 34. Winds, the effects of, in the diffusion of insects, 148. Wings of insects, subject to undue development in hot seasons, 43 ; liable to become gradually obsolete in islands, 81; more variable than other organs, 97. Xenostrongylus, its geographical distribution, 124; common to Madeira and Sicily, 139. Zargus pellucidus, Woll., variety of, on one of the Madeira Islands, 88. FINIS. Printed ly Taylor and Francis, Red Lion Court, Fleet Street. Lately published, by the same Author, in large 4to (with Thirteen Coloured Plates), price £2 2s., INSECTA MADERENSIA ; BEING AN ACCOUNT OF THE INSECTS oF THE ISLANDS OF THE MADEIRAN GROUP. London: Joun Van Voorst, 1, Paternoster Row.