726 The Colors of Animals and Plants. [ December, 
those general laws which lead to such superior developments 
even in domestic breeds; but in some cases the need of protec- 
tion by the female while incubating, to which I formerly imputed 
the whole phenomenon, may have suppressed a portion of the 
ornament which she would otherwise have attained. 
Another real though as yet inexplicable cause of diversity of 
color is to be found in the influence of locality. It is observed 
that species of totally distinct groups are colored alike in one 
district, while in another district the allied species all undergo 
the same change of color. Cases of this kind have been adduced 
by Mr. Bates, by Mr. Darwin, and by myself, and I have col- 
lected all the more curious and important examples in my Ad- 
dress to the Biological Section of the British Association ‘at 
Glasgow in 1876. The most probable cause for these simultane- 
ous variations would seem to be the presence of peculiar elements 
or chemical compounds in the soil, the water, or the atmosphere, 
or of special organic substances in the vegetation; and a wide 
field is thus offered for chemical investigation in connection with 
this interesting subject. Yet, however we may explain it, the 
fact remains of the same vivid colors in definite patterns being 
produced in quite unrelated groups, which only agree, so far as 
we yet know, in inhabiting the same locality. 
Let us now sum up the conclusion at which we have arrived 
as to the various modes in which color is produced or modified in 
the animal kingdom. 3 
The various causes of color in the animal world are molecular 
and chemical change of the substance of their integuments, Or . 
the action on it of heat, light, or moisture. It is also produced 
by interference of light in superposed transparent lamelle, or by 
excessively fine surface striae. These elementary conditions for 
the production of color are found everywhere in the surface 
structures of animals, so that its presence must be looked upon 
as normal, its absence as exceptional. oe 
Colors are fixed or modified in animals by natural selection for ; 
various purposes: obscure or imitative colors for concealment; = 
gaudy colors as a warning; and special markings: either for SS 
easy recognition by strayed individuals, females, or young, OY ee 
direct attack from a vital part, as in the large, brilliantly-marked — 
wings of some butterflies and moths. Se 
Colors are produced or intensified by processes of develop- : 
ment, — either where the integument or its appendages undergo — 
great extension or modification, or where there is a surplus of 
