SURVIVAL OF ORGANS 295 



are light-producing organs, and the fish are in 

 reality blind. This may be the case also in the 

 males of Machaerites. It may also be the case 

 that the male has an opportunity for using eyes 

 absent in the case of the female, the males some- 

 times leaving the caves, the females remaining 

 within them. Something analogous to this occurs 

 in the case of eels : the males remain always in 

 the sea while the females rejoin them only for 

 purposes of reproduction. Moreover, there is still 

 a third hypothesis, that the male of Machaerites be- 

 came an inhabitant of caves later than the female, 

 and has not yet had time for the loss of its eyes. 



2. Unfunctional organs which persist as rudiments. 



It is outside our purpose to discuss here the 

 numerous cases of organs reduced through adapta- 

 tion, such as the leaves reduced to serve as 

 protectors of young buds (Phyliocactus, fig. 78), or 

 the wings of the ostrich which, although much 

 reduced, are supposed to assist the bird in running. 

 The utility of such organs explains their persist- 

 ence ; we are concerned here with organs which, 

 although useless, persist in a reduced form. 



1. ABSENCE OF VARIATIONS. In discussing organs 

 which, although without function, have persisted in 

 a complete state, we attributed the persistence to 

 absence of variations. It is probable that the 

 same cause operates in maintaining useless vestiges. 



