Darwin and Modern Science [195]
observed by Darwin in 1832 at St Jago, Cape de Verd Islands, the first place visited during the voyage of the "Beagle". From Rio he wrote to Henslow, giving the following account of his observations, May 18, 1832: "I took several specimens of an Octopus which possessed a most marvellous power of changing its colours, equalling any chameleon, and evidently accommodating the changes to the colour of the ground which it passed over. Yellowish green, dark brown, and red, were the prevailing colours; this fact appears to be new, as far as I can find out." ("Life and Letters", I. pages 235, 236. See also Darwin's "Journal of Researches", 1876, pages 6- 8, where a far more detailed account is given together with a reference to "Encycl. of Anat. and Physiol.")
Darwin was well aware of the power of individual colour adjustment, now known to be possessed by large numbers of lepidopterous pupae and larvae. 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 was well aware of the power of individual colour adjustment, now known to be possessed by large numbers of lepidopterous pupae and larvae. 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.)