Trans. of Linn. Soc., p. 510. + Nat. Hist. Review, April 1863.

“ This principle can be no other than natural selection, the selecting agents being insectivorous animals, which gradually destroy those sports or varieties that are not sufficiently like Jthomie to deceive them.... Such, I conceive, is the only way in which the origin of mimetic species can beexplained. I believe the case offers a most beautiful proof of the truth of the theory of natural selection. It also shows that a new adaptation, or the formation of a new species, is not effected by great and sudden change, but by numerous small steps of natural variation and selection.”*

Two questions suggest themselves. 1. Why are the Helconide, which by their brilliant colouring attract the eye of insectivorous birds, and by their slowness on the wing are easily seized, mimicked more than other families of butterflies? and, 2. Why are insects so much more subjects of mimicry than other animals?

Both questions are answered by Bates. 1. As there is nothing apparent in the structure or habits of the Helicontde which could render them safe from persecution by the numerous insectivorous animals which are ever on the watch in the same parts of the forest which they inhabit, “it is probable that they are unpalatable to insect enemies. Some of them have exsertile glands near the arms, which are protruded when the insects are roughly handled; it is well known that similar organs in other families secrete fetid liquids or gases, and serve as a protection to the species. I never saw the flocks of slow-flying Helzconid@ in the woods persecuted by birds or dragon-flies, to which they would have been an easy prey; nor, when at rest on leaves, did they appear to be molested by lizards or the predaceous flies of the family Asz/zde, which were very often seen pouncing on butterflies of other families. If they owe their flourishing existence to this cause, it would be intelligible why the Leptalide, whose scanty number of individuals reveals a_ less protected condition, should be disguised in their dress, and thus share their immunity.” fT There can be little doubt that this is the explanation. Mr. Wallace adduces like evidence as to these skunks of the insect world. He says that the families of butterflies, Helicontde, Danaid@, and Acreide—including a thousand species characteristic of the three tropical regions, South America, South Asia, and Africa—“all have ample, but rather weak wings, and fly slowly; are very abundant, conspicuous in colours and markings, never try to conceal them-

Trans. of Linn. Soc., pp. 512, 513. + Jozd., p. 510, and infra, p. 106.

selves, and have juices which exhale a powerful scent, so that when one kills them by pinching the body, the liquid that exudes stains the fingers yellow, and leaves an odour that can only be removed by repeated washings.” * 2. The frequency and exactness of mimetic analogies in insects is explained by their having “perhaps attained a higher degree of specialisation, after their type, than most other classes, as seems to be shown by the perfection of their adaptive structures and instincts.” Their being more numerous and striking in tropical than in temperate countries is perhaps attributable to the more active competitive life,’ and immense fertility, “with more rapid succession of their generations in hot than in cold countries.” f Objections have been advanced against Bates’s explanation of mimicry, chiefly by naturalists whose conservatism retards their application of the theory of natural selection to every part of every organism; or whose pusillanimity causes them to wear a livery mimetic of old forms of belief, which enables them to pass muster with the orthodox. To the objection that mimicry is a special endowment for the protection of the animal, the answer that there are gradations of mimetic analogies is sufficient. To the objection that similar conditions produce the resemblances between the mimicked and the mimicker, the answer is that similar conditions act only on a small proportion of organisms, the mimetic analogies being limited to a few groups. To the objection that mimicry is produced by reversion to ancestral types, the answer is that the imitation is only in external and visible characters, and that the argument does not account for the mimickers and the mimicked tenanting the same areas. The basis of mimetic analogies lies in the origination of some slight variation in the mimicker which tends in the direction of likeness to the mimicked. Upon this variation natural selection operates. The reception given to Bates’s paper was most gratifying to him. Darwin heard it, and, on its publication, wrote as follows:{—

Darwinism, p. 234, and cf Mr. Poulton’s paper on ‘‘The Experimental Proof of the Protective Value of Colour and Markings in Insects,” especially Table, p. 262. Proc. Zool. Soc., March 1887. + Upon this, see Darwin’s letter next page, t This letter has been printed in the Zzfe and Letters, ii., 391.

Charles Darwin to H. W. Bates.

‘Down, BROMLEY, KENT, Woveméber 20¢h, 1862.

‘ DEAR BATES,*

‘‘T have just finished, after several reads, your paper. In my opinion it is one of the most remarkable and admirable papers I ever read in my life. The mimetic cases are truly marvellous, and you connect excellently a host of analogous facts. The illustrations are beautiful, and seem very well chosen; but it would have saved the reader not a little trouble if the name of each had been engraved below each separate figure; no doubt this would have put the engraver into fits, as it would have destroyed beauty of plate. Iam not at all surprised at such a paper having consumed much time. I rejoice that I passed over the whole subject in the Orzgzz, for I should have made a precious mess of it. You have most clearly stated and solved a wonderful problem. No doubt, with most people, this will be the cream of the paper; but I am not sure that all your facts and reasoning on varieties and the segregation of complete and semi-complete species is not really more, or at least as valuable a part. I never conceived the forces nearly so clearly before: one feels present at the creation of new forms.* I wish, however, you had enlarged a little more on the pairing of similar varieties; a rather more numerous body of facts seems here wanted. ‘‘Then again, what a host of curious miscellaneous observations there are, as on related sexual and individual variability you give; these will some day, if I live, be a treasure to me.

‘With respect to mimetic resemblances being so common with insects: do you not think it may be connected with their small size? They cannot defend themselves; they cannot escape by flight, at least from birds; therefore they escape by trickery and deception. I have one serious criticism to make, and that is about title of paper. I cannot but think that you ought to have called prominent attention in it to the mimetic resemblances. Your paper is too good to be largely appreciated by the mob of naturalists without souls, but rely on it, that it will have Jestizg value, and I cordially congratulate you on your first great work. You will find, I should think, that Wallace will fully appreciate it. How gets on your book? Keep your spirits up. A book is no light labour. I have been better lately and working hard, but my health is very indifferent. How is your health? ‘* Believe me, dear Bates, ‘* Yours very sincerely,

“ Ca. DAR WIN.’”

FHT. W. Bates to Charles Darwin.

‘‘ KING STREET, LEICESTER, JVovember 24th, 1862.

“My DEAR MR. DARWIN,

‘‘T am now well repaid for the labour of writing the paper in Linn. Trans., having received your warm and discriminating approval.

In his review of the paper, Darwin says: ‘It is hardly an exaggeration to say that whilst reading and reflecting on the various facts given in this Memoir, we feel to be as near witnesses, as we can ever hope to be, of the creation of a new species on this earth.”

Dr. Hooker has also written a most friendly letter on the subject, valuing the treatise highly. Mr. Wallace and I discussed the matter last time I was in London, and he thinks me entirely right. As for the ‘mob’ of naturalists, I don’t care much about them. There is only one man in Europe who will be able to follow my reasonings, species by species and variety by variety; this is Dr. C. Felder, of Vienna, and I shall be glad to hear from him upon the subject. As to ordinary entomologists, they cannot be considered scientific men, but must be ranked with collectors of postage-stamps and crockery. ‘‘T wish to have more criticisms from you on the subject when you are quite at leisure. (What anidea!) Iam sure I could now put the case much more strongly. But you say the argument is quite clear, so I must rest contented. I now believe one of the forms of Leptalis (L. Argochloe) is not an immediate descendant from L. Theonoé, as the other varieties are, but has originated (in a similar way) somewhere westward, in Andean valleys, and has wandered to the Amazons. It would be tedious here to give reasons. Does it occur to you that a great deal may be unexpectedly learnt by thus thoroughly going into one small group of natural objects? The more I study them the more I am surprised at the wonderful revelations which spring from them: much more than is explained in my treatise....”

The following is,the letter from Dr. Hooker, to which Bates refers:—

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

“‘ Kew, LVovember 13th, 1862.

‘““ My DEAR MR. BATES,

“‘One line to say how greatly I am delighted with your paper in the Linnean. I hope indeed that you will give us another. It is a most invigorating essay, and will, I am sure, please Darwin vastly. I like both the conception and execution of it, and hope you find that our society has done justice to the paper. ‘‘T have only one criticism: at page 508, where, line 10, you say-cautiously enough—that ‘similar varieties in two (already)* nearly allied forms do sometimes show that they have been affected (in a similar way) * by physical conditions,’ and you go on to quote seaside habitat.- Now I do not see how you apply Akyszcal conditions here, logically, as a cause different in kind and operation from zafural conditions elsewhere. After all seaside is only, in other words, ‘conditions only found near sea’—not necessarily the seaside itself at all. If the physical conditions of sea act at all, they can only act as natural conditions do by favouring races, e.g., you would perhaps say that sea atmosphere and succulent habits of plants, going so often together, was sign of plants being affected by physical conditions. I say: Not at all. It only shows that those varzefzes alone which are so constructed as to resist the effects of superabundant humidity have survived. We know em{Zzrically

These words are omitted in Dr. Hooker’s letter. t Bates’s words are: “ A great number of insects are modified in one direction by a seaside habitat.”

(and thus only) that such a physique goes with a succulent habit, and therefore, 27 other words, the succulent varieties alone are favoured. The ‘ modification in one way of plants by seaside habitat’ is not, in so far as the plant is concerned, different from your ‘modification in another way of insects by action of predaceous enemies.’ In either case the struggle for life comes into play, but less markedly in the seaside habitat case. This is a very small criticism, but then it is my only one, and so must make most of it! How goes on the book? I have been dreadfully busy all summer, and wish I were in touch with you, and knew when my daily work ended. ‘* Ever sincerely yours, ** fos: D, HOOKER,”

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