olour 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 Researc