190 FERNANDUS PAYNE. 



is too short or whether they have reached a fixed condition in 

 so far as variations toward adaptations for a cave life are con- 

 cerned. We might extend it a httle further and ask whether all 

 animals would lose their color or whether their eyes would de- 

 generate in a cave environment? In other words, is the environ- 

 ment alone responsible for the present condition of cave animals 

 or is there an internal orthogenetic factor at work to which the 

 environment serves as a stimulus? Eigenmann in his discussion 

 of the origin of cave animals has stated that forms which now 

 inhabit caves were predestined to become cave animals long 

 before they ever entered a cave. That is, they had varied in a 

 certain fixed direction, and these variations had tended to fit 

 them for a cave existence. If such is the case, would the present 

 cave animals have become blind and colorless if they had not 

 entered caves ? 



