DISUSE AND ITS EFFECTS. 



39 



membrane occupying the space known as the pupil of 

 the eye. This membrane rapidly atrophies and the 

 pups begin to see. In the human offspring a precisely 

 similar membrane is present during em- 

 bryonic life, but atrophies a few weeks 

 before the termination of intra-uterine life. 

 The mode by which fcetal or larval organs 

 of this character are slowly removed will 

 be considered in detail in a later chapter. 

 Suppression of Parts. It has long been 

 known that in the embryo of vertebrates 



TAIL 



SP1RACUE 



EYE MOUTH 



ASCIDIAN 



NOTOCHORD 



BRAIN 



FIG. 



19. Ascidian Tadpoles (after Lankester). 

 adult ascidian. 



A, An 



many structures and organs are formed and then dis- 

 appear without attaining, as far as our knowledge allows 

 us to judge,, a functional condition. 



