4 LABORATORY MANUAL FOR VERTEBRATE ANATOMY 



covered with scales for protective purposes, but these scales are not the same morphologically 

 because they originate from the skin in different ways. Such functional correspondences are 

 usually the result of environmental conditions, i.e., they are "adaptations. " Not only parts of 

 animals but whole animals may come to resemble each other through the action of the same 

 environment, as whales and fishes. Such resemblance, not based on actual relationship, is 

 called convergence. On the other hand, animals closely related to each other may differ greatly 

 in appearance, owing to the different environments in which they live, as seals and cats. This 

 is known as divergence. (See further, N, pp. 15-20; W, pp. 16 ff.) 



