76 



EVOLUTION, GENETICS, AND EUGENICS 



Plica 

 Semilunaris 



^%^-x 



JVl/J/f 



Wflpf 



Fig. q. — Illustrations of the nictitating membrane in the various animals 

 named, drawn from nature. The letter N indicates the membrane in each case. 

 In man it is called the plica semilunaris and is represented in the two lower drawings 

 under this name. In the case of the shark (Galeus), the muscular membrane is 

 shown as dissected. {From Romanes.) 



