The Problem of Adaptation 23 
animals in protecting them from attack. In the case of cer- 
tain bacteria it seems quite evident that the production of 
light can be of no use as such tothem. The production of 
light may be only a sort of by-product of changes going on 
in the organism, and have no relation to outside conditions. 
In certain cases, as in the glowworm, it has been supposed 
that the display may serve to bring the sexes together; but 
since the phosphorescent organs are also present in the larval 
stages of the glowworm, and since even the egg itself is said 
to be phosphorescent, it is improbable, in these stages at least, 
that the presence of the light is of service to the organism. 
It has been pointed out that the colors of certain animals 
may serve to conceal them and may be regarded as an 
adaptation ; but it is also true that in many cases the color of 
the whole animal or the color of special parts can be of little 
if any direct use. While it is difficult to show that the 
wonderful patterns and magnificent coloration of many of the 
larger animals are not of service to the animal, however 
sceptical we may be on the subject, yet in the case of many 
microscopical forms that are equally brilliantly colored there 
can be little doubt that the coloration can be of no special 
service to-them. If it be admitted that in these small forms 
the color and the color patterns are not protective, we should 
at least be on our guard in ascribing off-hand to larger forms 
a protective value in their coloration, unless there is actual 
-proof that it serves some purpose. 
We also see in other cases that the presence of color need 
not be connected with any use that it bears as such to the 
animal. For instance, the beautiful colors on the inside of 
the shells of many marine snails and of bivalve mollusks, 
can be of no use to the animal that makes the shell, because 
as long as the animal is alive this color cannot be seen from 
the outside. This being the case let us not jump too readily 
to the conclusion that when other shells are colored on the 
outer surface that this must be of use to the mollusk. 
