On his arrival in England, he set to work upon his extensive collections. The larger portion of these gradually passed into private hands in different parts of Europe. Those which had been purchased by the British Museum had the advantage of his detailed arrangement, involving frequent journeys to London, where, as will be seen, after vain attempts to procure permanent employment as a naturalist, he finally settled. Meanwhile his pen was as busy as his hand in communicating the results of his classificatory work to learned societies. In March 1860 (four months after the publication of the Orzgin of Species, it may not be amiss to note) he began a series of papers entitled “ Contributions to an Insect Fauna of the Amazon Valley,” which were printed in the Zvansactions of the Entomological Society. These were at first devoted to a new classification of the Diurnal Lepidoptera (in untechnical language, butterflies), founded chiefly on the structure of the anterior legs, a classification which has been very generally adopted by entomologists.*

As the subjoined letters show, Bates, not being, as Darwin said, of “the mob of naturalists without souls,” did not stop at classification, but passed on to the consideration of larger questions to which it and other evidence pointed. -He had the saving grace of the sense of relation, lacking which, the observer only “sees men as trees walking.” In the words of Professor Huxley in his last presidential address to the Royal Society: “That which the investigator perceives depends much more on what lies behind his sense-organs than on the object in front of them.” In the papers

Trans. Entomological Society, vol. v., 1858-61, p. 350.

just cited Bates goes on to show that, where no great variety of elevation or natural barriers exist, minor climatic conditions influence the fauna and flora of a country in their effect on soil, which in its turn affects vegetable and animal life. He remarks that the distribution of the species of Papzlzo (cne of the lowest families of butterflies) affords strong ground for considering the Guiana region as possessing productions of peculiar character, and a “ very large proportion of species peculiar to itself; the numerous local sub-specics peculiar to the Amazons all showing themselves to be local modifications of Guiana species,” so that Guiana is probably “the great centre whence radiated the species which now people the low land on its borders.”* Then he discusses the more abstruse question of Geographical Distribution, and gives reasons for dissenting from the current theories of an extension of the Glacial Epoch to equatorial regions,t whereby many species of temperate zones would be enabled to pass from the northern to the southern hemisphere:—

‘‘It is supposed that at that time the climate of the equatorial plains resembled what now exists at six or seven thousand feet of elevation near the equator. It is a tolerably well-established fact that arctic forms then moved twenty-five. degrees southward from their homes, and if the decreased temperature then extended to the centre of the tropics, the regions near the equator must have possessed a temperature similar to what is now enjoyed in countries near the twenty-fifth parallel of latitude. Extinction in this case must have been at work largely amongst the forms (if there were any) peculiar to the equatorial zone, and the present character of its fauna ought to show, in consequence, a poverty in endemic forms, and unmistakable signs, in the shape of local varieties or representative species, of a dependence, on the part of the now existing forms, on those living towards the twenty-fifth parallel of latitude; because, with the returning warmth, the extra-tropical species then living near the equator would retreat north and south to their former homes, leaving some of their congeners, slowly modified subsequently by the altered local conditions, to re-people the zone they had forsaken. The present distribution of the species of agz/z0 does not support the hypothesis of such a degree of refrigeration in the equatorial zone of America, or, at least, does not countenance the supposition of any considerable amount of extinction.{ The fauna of the Guiana-Amazonian region, so far as regards this genus, is in the highest degree peculiar; showing no dependence on that of the countries near either ofthe tropics. If now we except the local varieties (the inclusion of which would only strengthen the position), there are about

See infra, pp. XxXxv., 54. } See zzfra, p. lxxxi. t “There is no proof whatever of glaciation in any part of Brazil.”—Wallace’s Darwinism, p. 370.

Xxxii MEMOIR.

forty perfectly distinct species of this genus inhabiting this region, and of these no less than eighteen are endemic, all of them so peculiarly restricted in their range that they are not found, nor any forms closely representing them, even at twelve degrees of latitude on either side of the equator. The result is plain, that there has always (at least through immense geological epochs) been an equatorial fauna rich in endemic species, and that extinction cannot have prevailed to any extent within a period of time so comparatively modern as the glacial epoch in geology.’’ *

This new aspect of the matter deeply interested Darwin. In his chapter on “Geographical Distribution” in the Ovigzz of Species, he had explained the presence of north temperate forms, chiefly plants, in the highlands of the southern hemisphere, as due “to a lowering of temperature during glacial epochs, which allowed these forms to migrate across the intervening tropical lowlands.” But, as Mr. Wallace points out, any such change within the epoch of existing species is almost inconceivable, the wind-carriage, and, in far lesser degree, the bird-carriage, of seeds explaining the distribution without assuming the agency of vast physical changes.T

The following correspondence deals with this question:—

“Down, BROMLEY, KENT, JZarch 26fh, 1861.

(Have you received copy of new edition of Origin?) “DEAR SIR, “I have read your papers with extreme interest, and I have carefully read every word of them. They seem to me to be far richer in facts on ‘variation, and especially on the distribution of varieties and sub-species, than anything which I have read. Hereafter I shall re-read them, and hope in my future work to profit by them and make use of them. The amount of variation has much surprised me. The analogous variation of distinct species in the same regions strikes me as particularly curious. The greater variability of female sex is new to me. Your Guiana case seems in some degree analogous, as far as plants are concerned, with the modern plains of La Plata, which seem to have been colonised from the north; but the species have been hardly modified. I have been particularly struck with your remarks on the glacial period. You seem to me to have put the case with admirable clearness and with crushing force. I am quite staggered with the blow, and do not know what to think. Of late several facts have turned up, leading me to believe more firmly that the glacial period did affect the equatorial regions, but I can make no answer to your arguments, and am completely in a cleft stick. By an odd chance I had only a few days ago been discussing the subject, in relation to plants, with Dr. Hooker, who believes to a certain extent; but strongly urged the little apparent extinction in equatorial regions. I stated in a letter, some days ago, to him that the |

Trans Entom. Soc., vol. V., pp. 352, 353- t+ Cf. Darwinism, pp. 371-3-

tropics of South America seem to have suffered less than the Old World. There are many perplexing points; temperate plants seem to have migrated far morethan animals. Possibly species may have been formed more rapidly within tropics than one would have expected. I freely confess that you have confounded me, but I cannot yet give up my belief that the glacial period did to a certain extent affect the tropics.... You will, I think, be glad to hear that I now often hear of naturalists accepting my views more or less fully; but some are curiously cautious in running risk of any small cdium in expressing their belief. With cordial thanks and respect, believe me ‘Yours sincerely,

**C, DARWIN.”’

HT. W. Bates to Dr. F D. Hooker.

‘KING STREET, LEICESTER, March 19th, 1861.

‘ DEAR SIR,*

‘‘Having had the honour of an introduction to you (at the Lin. Soc.), I feel I am not taking a liberty in forwarding for your perusal a paper I have just published on the subject of the Amazonian Insect Fauna (the first of a series), wherein some important generalisations are introduced. They arise from the review of the species, and, as you will perceive, are chiefly on the subjects of the relations of the fauna, the variation of species, and especially the persistency of varieties once formed, probably by local isolation, after they have been brought by natural redistribution into contact with fellow varieties. ‘‘T know you are one of the very few who have lately striven against much opposition to elevate natural history into the rank of an inductive science. It certainly has not been one hitherto, but merely the observation and cataloguing of facts. An immense multitude of curious, isolated facts, the significance of which has been dimly seen by their observers, have been accumulated; but they are unfruitful, simply because ofthe foregone and illogical conclusion that species are absolute and immutable.

‘In a little paper I have written (not published), I have thought of comparing natural history under these circumstances with the state of astronomy before Copernicus. For in the same way that all astral observations were barren whilst the earth was conceived to be flat, so all natural history facts lead to no real enlargement of knowledge whilst species are held to be absolutely created as they now stand. ‘*The Ptolemean theory of revolving spheres also, I think, is quite a parallel case with the circular theories of Swainson, etc. ‘**T am afraid I have done wrong in commencing to publish in a periodical of limited circulation. This, amongst other disadvantages, compels me to send copies for perusal to those who otherwise would not hear of the papers. ‘‘T have accumulated a vast amount of material during my eleven years’ travels on the Amazons, and during the whole time directed my attention to the modifications of species and kindred subjects; but I have had so little countenance from scientific men since my return, as not to feel inclined to publish at all.

‘‘T have sent a copy to Mr. Darwin and to Mr. P. L. Sclater. Hoping that you may find time to read my paper and give me your opinion thereupon, ‘« Believe me yours,

“HH. W. BARES

In his reply to this letter Dr. Hooker wrote encouragingly, as follows:—

‘‘T thank you very much for the papers on the Amazonian Insect Fauna, which you have been good enough to send me. They seem to my judgment to be extremely well done, and they are most interesting and suggestive. I do not see how any accurate conclusions as to the migrations of species can be worked out without following the method you have pursued, and I suppose, as far as insects at least are concerned, have originated. Those you have arrived at appear to be logically and scientifically secure, and as such are great gains. I quite agree with all you say about the necessity of distinguishing varieties as well as species.... I began science myself with entomology, but could not keep it up with botany, so as to do any good to either; but I was much struck in my small experience with the ample facility there was for working out questions of variation, owing to the readiness with which you can compare many specimens at one coup d@’zl, and sort them in various diverging series. With plants this is almost impossible, except by covering the floor, or very large tables, which is the way I adopt.’’

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