An excellent example was brought to his notice by C.V. Riley ("More Letters" II, pages 385, 386.), while the most striking of the early results obtained with the pupae of butterflies--those of Mrs M.E. Barber upon Papilio nireus--was communicated by him to the Entomological Society of London. ("Trans. Ent. Soc. Lond." 1874, page 519. See also "More Letters", II. page 403.)It is also necessary to direct attention to C.W. Beebe's ("Zoologica: N.Y.
Zool. Soc." Vol. I. No. 1, Sept. 25, 1907: "Geographic variation in birds with especial reference to the effects of humidity".) recent discovery that the pigmentation of the plumage of certain birds is increased by confinement in a superhumid atmosphere. In Scardafella inca, on which the most complete series of experiments was made, the changes took place only at the moults, whether normal and annual or artificially induced at shorter periods. There was a corresponding increase in the choroidal pigment of the eye. At a certain advanced stage of feather pigmentation a brilliant iridescent bronze or green tint made its appearance on those areas where iridescence most often occurs in allied genera. Thus in birds no less than in insects, characters previously regarded as of taxonomic value, can be evoked or withheld by the forces of the environment.
WARNING OR APOSEMATIC COLOURS.
From Darwin's description of the colours and habits it is evident that he observed, in 1833, an excellent example of warning colouring in a little South American toad (Phryniscus nigricans). He described it in a letter to Henslow, written from Monte Video, Nov. 24, 1832: "As for one little toad, I hope it may be new, that it may be christened 'diabolicus.' Milton must allude to this very individual when he talks of 'squat like a toad'; its colours are by Werner ("Nomenclature of Colours", 1821) ink black, vermilion red and buff orange." ("More Letters", I. page 12.) In the "Journal of Researches" (1876, page 97.) its colours are described as follows: "If we imagine, first, that it had been steeped in the blackest ink, and then, when dry, allowed to crawl over a board, freshly painted with the brightest vermilion, so as to colour the soles of its feet and parts of its stomach, a good idea of its appearance will be gained.""Instead of being nocturnal in its habits, as other toads are, and living in damp obscure recesses, it crawls during the heat of the day about the dry sand-hillocks and arid plains,..." The appearance and habits recall T.
Belt's well-known description of the conspicuous little Nicaraguan frog which he found to be distasteful to a duck. ("The Naturalist in Nicaragua"(2nd edition) London, 1888, page 321.)
The recognition of the Warning Colours of caterpillars is due in the first instance to Darwin, who, reflecting on Sexual Selection, was puzzled by the splendid colours of sexually immature organisms. He applied to Wallace "who has an innate genius for solving difficulties." ("Descent of Man", page 325. On this and the following page an excellent account of the discovery will be found, as well as in Wallace's "Natural Selection", London, 1875, pages 117-122.) Darwin's original letter exists ("Life and Letters", III. pages 93, 94.), and in it we are told that he had taken the advice given by Bates: "You had better ask Wallace." After some consideration Wallace replied that he believed the colours of conspicuous caterpillars and perfect insects were a warning of distastefulness and that such forms would be refused by birds. Darwin's reply ("Life and Letters", III. pages 94, 95.) is extremely interesting both for its enthusiasm at the brilliancy of the hypothesis and its caution in acceptance without full confirmation:
"Bates was quite right; you are the man to apply to in a difficulty. Inever heard anything more ingenious than your suggestion, and I hope you may be able to prove it true. That is a splendid fact about the white moths (A single white moth which was rejected by young turkeys, while other moths were greedily devoured: "Natural Selection", 1875, page 78.); it warms one's very blood to see a theory thus almost proved to be true."Two years later the hypothesis was proved to hold for caterpillars of many kinds by J. Jenner Weir and A.G. Butler, whose observations have since been abundantly confirmed by many naturalists. Darwin wrote to Weir, May 13, 1869: "Your verification of Wallace's suggestion seems to me to amount to quite a discovery." ("More Letters", II. page 71 (footnote).)RECOGNITION OR EPISEMATIC CHARACTERS.
