EMBRYOLOGY OF ECIIINODERMS. 



133 



180 and 181 we have different stages of the little Sea-urchin, with 

 its spines and suckers of a large size and in full activity. The 



Fig. 177. 



Fig. 178. 



Fig. 179. 



appearance of the Sea-urchin, as soon as this larva or Pluteus is 

 completely absorbed, is much more like that of the adult than is 

 the Star-fish at the same stages, in which, as we have seen, there 

 is a transition period of considerable duration. 



Fig. 177. Fig. 176 seen endways. 



Fig. 178. The Sea-urchin resorbing the arms of the larva. 



Fig. 179. Half a young Sea-urchin immediately after resorption of the larva ; s" s" spines, t' t' am- 

 bulacral tentacles. 



