52 



BRANCH ECHINODERMATA 



near the coast, where the ova are fertilized in the water. Echino- 

 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 



ardiac stomath 

 intestinal caecum 



muscles of the pylorti caeca. 



eye spot -- 



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- 



