132 



MARINE ANIMALS OF MASSACHUSETTS BAY. 



Fig. 176 the young Sea-urchin has so far encroached upon the 

 Pluteus that it forms the essential part of the body, the arms and 



Fig. 170. 



rods appearing as mere appendages. Fig. 177 shows the same 

 animal when we looked down upon it in its natural attitude ; the 

 Sea-urchin is carried downward, and the arms stretch in every di- 

 rection around it. In Fig. 178 the Pluteus is already in process 

 of absorption ; in Fig. 179 it has wholly disappeared ; in Figs. 



Fig. 176. Adult larva of Toxopneustes, / brachilar appendages. 



