EVIDENCES FROM MORPHOLOGY 



147 



TK^X 



Fig. 19. — 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 (Galetis), the muscular membrane is 



shown as dissected. {From Romanes.) 



