202 Variations and Orthoplasy 



functions ; and its influence may be diverse, according as 

 this or that animal, differing from others in his correlations, 

 finds himself able to use it. It has been said above that 

 divergent lines of evolution may spring up because fostered 

 by one and the same accommodation. This means that the 

 division of an animal into set characters is at the best arti- 

 ficial ; the whole animal lives or dies, and some slight 

 utility here, or another slight utility there, will give natural 

 selection its chance on this individual or that for the em- 

 phasis of this character or that. The correlated characters 

 are just as truly screened and fostered, and helped over 

 the hard places, by organic selection as are the coincident 

 characters. And such is the plasticity of the organism 

 that such characters may be pressed into service for 

 utiHties ' not dreamed of ' in the original function by which 

 they may have been kept alive. 



§ 3. Illustrations of Orthoplasy with Correlated Variation 



Let us take as illustration the case of the evolution of 

 the sole, the adaptation of whose eyes has already been 

 remarked upon (p. 164). This adaptation is part of a larger 

 and more complex one. Indeed, the placing of both eyes 

 on the same side has utility only to an animal which lies 

 on one side near the ground, and so does not require an 

 eye on the under side ; this position — flat on one side — 

 is therefore the adaptation in connection with which the 

 position of the eyes has its utility. But why is it use- 

 ful to the sole to lie on one side near the bottom .? — why 

 this adaptation } This is explained again, in turn, by an- 

 other adaptation, that of concealment from enemies, and 

 for this utility we find another series of correlated 

 changes, those of protective coloration — the under side 



