236 



Dzvellers of the Sea and Shore 



hatch, a striking revelation greets us in the appearance 

 of tlie embryo. It has become ciistinctly trilobate in 

 character. As in the trilobite, a highly arched ridge 

 runs lengthwise over the middle region of the body, the 

 sutures between the segments of the hind body are 

 somewhat bent, and the outer edge, or lateral plate, 

 of each segment Is strongly convex. 



^'^^•■'- ■:■■.'■■■■•■.■' ■ ■■'■ ■ — . ■ • • A-'' ■-■ ■;-;-<':^i; 



./<?-;, 



,.A??f;•^s^;:::■v\:.;.:.^ •■» 





TRILOBITELIKE LARVA OF THE HORSESHOE CRAB. 



Finally the membrane ruptures and liberates the 

 larva. The larva differs from the embryo in that the 

 abdomen is broader and flatter, and that the sutures 

 between the lateral plates have disappeared, leaving 

 segmented only a keellike middle ridge. It is now a 

 little more than a tenth of an inch in length and a trifle 

 less in breadth. Immediately it shows great activity 

 by vigorously striking out into the water and swimming 

 away. For about three weeks it lives a more or less 

 nomadic life, wandering widely in this period, when at 

 the end it molts and settles to the floor for good. Witii 



