52 



BRANCH ECHINODEUMATA 



near the coast, where the ova are fertihzed in the water. Echiuo- 

 derms of the same species are often gregarious. 



The water-vascular system is a marked characteristic of 

 echinoderms (Fig. 41). It begins externally with the cal- 



-eye spot 



eye spot ■ 



Pyloric itutitm 

 'muscles of ike pyloric caeca 

 Fig. 41. — Dissection of a starfish {Asterias sp.)- (From Kellogg.) 



careous perforated madreporic plate which is connected by a 

 calcareous (Stone) canal with the central ring around the 

 mouth, from which tubes proceed along each arm, in the star- 



