1877.] The Colors of Animals and Plants. 649 
the color of the soil wherever they are found, while several cater- 
pillars which feed on two or. more plants vary in color accord- 
ingly. Several such changes are quoted by Mr. R. Meldola in 
a paper on Variable Protective Coloring in Insects,! and some 
of them may perhaps be due to a photographie action of the re- 
flected light. In other cases, however, it has been shown that 
green chlorophyll remains unchanged in the tissues of leaf-eating 
insects, and being discernible through the transparent integument 
produces the same color as that of the food plant. 
These peculiar powers of change of color and adaptation are, 
however, rare and quite exceptional. As a rule there is no direct 
connection between the colors of organisms and the kind of light to 
which they are usually exposed. This is well seen in most fishes 
and in such marine animals as porpoises, whose backs are always 
dark, although this part is exposed to the blue and white light 
of the sky and clouds, while their bellies are very generally 
white, although these are constantly subjected to the deep-blue 
or dusky-green light from the bottom. It is evident, however, 
that these two tints have been acquired for concealment and pro- 
tection. Looking down on the dark back of a fish it is almost 
invisible, while to an enemy looking up from below, the light 
under surface would be equally invisible against the light of the 
clouds and sky. Again, the gorgeous colors of the butterflies 
which inhabit the depths of tropical forests bear no relation to 
the kind of light that falls upon them, coming as it does almost 
wholly from green foliage, dark-brown soil, or blue sky ; and the 
bright under wings of many moths, which are exposed only at 
night, contrast remarkably with the sombre tints of the upper 
Wings, which are more or less exposed to the various colors of 
surrounding nature. 
We find, then, that neither the general influence of solar light 
and heat nor the spécial action of variously-tinted rays are ade- 
qüate causes for the wonderful variety, intensity, and complexity 
Of the colors that everywhere meet us in the animal and vegeta- _ 
ble world. Let us, therefore, take a wider view of these colors, 
grouping them into classes determined by what we know of their 
~ Actual uses or special relations to the habits of their possessors. 
. This, which may be termed the functional or biological classifica- 
tion of the colors of living organisms, seems to be best expressed 
; by a division into five groups, as follows : — 
i 1 Proceedings of the Zoölogical Society of London, 1873, page 153. 
