446 



KADIATA: ECHIXODKUMATA. 



At the termination of each of the five belts or zones of 

 ambulacral plates there is a little triangular plate with a 

 minute opening which marks the place of the eye. Al- 

 ternating with the eye-plates are five larger plates, each 



FIG. 675. 



FIG. 674. 



Sea-Urchin, Toxopneustes drobachiensis, 

 Ag. Both coasts of the United States, 

 at the North. 



7 



Top view of Sea-Urchin, spines 

 removed. Shows ambniacral 

 and interanibulacral plates. 



perforated with a larger hole, through which the eggs are 

 laid. One of these plates is larger than the others, and 

 is filled with very minute holes, and is called by natural- 

 ists the madreporic body. It is believed to serve as a fil- 

 ter to the water which passes through it into the body of 

 the animal. 



The mouth is in the under side, and is armed with five 

 strong pointed and polished teeth, which form the outer 

 part of a remarkable dental apparatus, which is called 

 Aristotle's lantern. 



In a Sea-urchin of ordinary size there are five or six 

 hundred plates, all fitting together in the most perfect 

 manner, and bearing more than four thousand spines ; 

 and the suckers number about two thousand ! 



Besides the spines and the suckers, there are scattered 

 over the body and around the mouth of the Sea-urchin a 



