52 



BRANCH ECHINODEEMATA 



near the coast, where the ova are fertihzed 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- 



-cye spot 



^yliinc I iit'i ri'ii 

 ' mvsclci of the pyloiic coica ' * ' '^^ 



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



careous perforated marlreporic i)latc which is connected h\ a 

 calcareous (Stone) can;d with tlu^ central ring around the 

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



