THE SEA-URCHIN 41 



ture of animal matter. The shell itself consists of 

 geometrically arranged plates, joined together with 



Fig. 6. Parts of Sea-Urchin. Reduced. 



marvellous exactness, and covered with about 4,000 

 spikes, every one of which is beautiful to the minutest 

 detail. Mr. Saville Kent tells us, that in many of 



