V-* Qi\ ^ *. ' '' - s tfl %- ^ K- I ^ ^ ^ * .- -i ^C X -\ x ,% I *% . < ^ V 1 k. ^ Ov ^ \s* ^-e \\^ c^ -i v s|| i& ^> ^ x^ '\ry' ^ v ^ :' N5 \ A %- V?. %O xV '/ <^ ^ V V ^ \ o > f/ ^ x^^ltii^ \*fr f^ ">k ^ \ ^ \ \ ^ <v */,, ^ >> ^k c^ rv ^-^ s&fttl. INC P^ s^r "V* ,;#>^ololvS>iS X' ,^ ,/ft >> ^r 5C. ON THE VARIATION OF SPECIES WITH ESPECIAL REFERENCE TO THE INSECTA- FOLLOWED faY AN INQUIRY INTO THE NATURE OF GENERA X \ VEftNON WOLLASTON, M.A., F.L.S. " No compound of this earthly ball Is like another, all in all." TENNYSON. V v- LONDON: ?' . .- JOHN VAN VOOEST, PATERNOSTER ROW. 1856. " I do not enter so far into the province of the logicians as to take notice of the dif- ference there is between the analytic and synthetic methods of coming at truth, or it whether it is better to the from the or the proving ; begin disquisition subject, from 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 demonstration or argument 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. 1/22). ^HS PRINTED BY TAYLOR AND FRANCIS, RED LION COURT, FLEET STREET. TO CHAELES DARWIN, ESQ., M.A., V.P.E.S., Whose researches, in various parts of the world, have added so much to our knowledge of Zoological geography, this short Treatise is dedicated. PREFACE. is To make a dry subject entertaining, impossible ; has but to render it, at any rate, readable, 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- in the Madeira ing causes) which my researches 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 VI on the volume a more practical interest, for the general naturalist . to One of my main objects, however, has been call attention to the fact, that the Annulosa have the not been hitherto sufficiently considered, in great questions arising out of the distribution of animals and so plants ; hoping that, by 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 about or if I brought ; 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. I. CHAPTER Page Introductory Remarks CHAPTER II. Fact of Variation 7 As a matter of experience 8 As probable from analogy 10 CHAPTER III. Causes of Variation 19 1. Climatal causes generally (whether dependent upon latitude or upon altitude) 23 2. Temporary heat or cold, of an unusual degree ... 42 3. Nature of the country, and of the soil 46 4. Isolation; and exposure to a stormy atmosphere . 70 CHAPTER IV. Organs and Characters of Variation 95 CHAPTER V. Geological Reflections Ill CHAPTER VI. The Generic Theory 157 CHAPTER VII. Conclusion 181 CORKIGENDUM. Page 90, for Pecteropus Maderemis read Pecteropv.s rostratu-s. 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 the less we seem to know. know ; though 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 still will for elude his him ; nor she even once grasp, provided he be content to receive her as she is, instead of endeavouring to mould her to his preconceived ideas B 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 of ever been dis- unsolved ; nor indeed have some them cussed at all, except in a desultory manner and with insufficient data to reason from. Foremost amongst these, numerous problems affecting the distinction be- " " " '' tween varieties and species (as usually accepted) of the animal kingdom stand pre-eminent, especially in the Annulose Orders, in which those distinctions are less easy, a 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 circumstances 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 hints on the fact throw out a few general ; first, of aber- as a matter of ration, mere 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 latter also, it being scarcely possible to attach the proper value to an effect without first investigating its cause. The importance of assigning its legitimate weight (and that only) to a variety, is perhaps the most difficult task which the historian has to since on it natural accomplish ; 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 still less I wish to that the causes end ; would imply 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 as a hence I the informa- iient) specific one ; and gather tion that a reviewal of our first principles is occasionally necessary, if we would not restrict (however gradual and imperceptibly) that legitimate freedom which Nature 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- r lationship amongst all its members w hich 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 t\ie admission of it is almost necessary, in order to convey to our minds any definite notion of the word "species "at all : and that, lience, whilst I would not \vish to reject the hypothesis 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.