A ''Lhing FossiF' 



237 



this molt it loses entirely its segmented appearance and 

 now more nearly resembles the adult. A short spine- 

 like tail adorns the abdomen; the abdomen is thin, and 

 this region, like the cephalothorax, is hollowed out 

 underneath, the whole forming an ample shield for the 

 legs and gill feet. 



HORSESHOE CRAB MOLTING. 



When Limulus is a year old it attains to an inch in 

 length; by then it has molted several times. But not 

 before it is in its fourth year does it reach sexual ma- 

 turity. In that event the male acquires the strong front 

 claws that distinguish his sex. 



Thus, in following the development of Limulus, we 

 see revealed with remarkable distinctness its ancient 

 origin. It is not always so easy, however, to trace the 



