VESTIGIAL ORGANS 



In many cave animals the eyes are vestigial. Thus in a 

 number of cave fishes the eyeballs are small, spherical bodies 

 hidden under the skin and are of no use whatever. The 

 eyes of certain subterranean crayfishes, insects, and salaman- 

 ders are similarly useless and hence vestigial. 



Snakes are commonly regarded as legless reptiles. But in 

 the python (Fig. 2) a small claw 

 can be see on each side of the vent, 

 and these claws are supported by 

 bones within the body in such a 

 way that they are clearly vestiges 

 of hind legs. 



Snakes are also peculiar in the 

 structure of their lungs. Most air- 

 inhabiting vertebrates have two 

 lungs, one right and the other left. 

 Many snakes have only the right 

 lung, the left being represented 

 only by a small protuberance. 



Vestigial organs are also well 

 exemplified in birds. The ovaries 

 and oviducts of most animals are 

 evenly placed and equally developed 

 on the two sides of the body, but 

 in the birds these parts are func- 

 tional only on the left side (Fig. 3). The ovary and the 

 oviduct of the right side are abortive and quite useless, and 

 hence vestigial. 



The wings of certain birds are also vestigial. Wings used 

 as organs of flight are among the most striking possessions 

 of birds. Yet in the running birds, such as the ostrich and 

 the cassowary, the wings are entirely useless for flight, for 

 these birds are unable to rise off the ground. Relatively 



[37] 



Fig. 3. — Reproductive 

 organs of a female 

 pigeon. O, Left ovary; 

 Od, left oviduct; V, ves- 

 tigial right oviduct. After 

 Parker. 



