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 to them. 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; 



