244 



ZOOLOGY 



The radial nerves send branches to the tube-feet, from the base 

 of which a nerve passes to the sub-epidermal plexus of nerve 



14- 



FiG. 146.- 



-Diagrammatio vertical section of a Sea Urchin (from Leuokart). 

 After Hamann. 



fibrils, which ramify all over the body just outside the calci- 

 fications, and govern the movement of the pedicellariae and 

 spines. 



The generative organs typically consist of five arborescent 

 glands, though the number is often reduced, lying interradially, 

 and opening on the genital plates. In the young they are all 

 connected by a circular genital rhachis ; they become very 

 conspicuous in the breeding season. 



The pore plates of the paired ambulacral areas are in the 

 female Memiaster phiLvppii extended and depressed so as to 

 form four deep oval cups. In these the eggs are deposited 



