The wonderful power of rapid colour adjustment possessed by the
cuttle-fish was 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.