IX 



PHYLUM ANNULATA 



197 



Nereis is unisexual. The sexual elements, ova or sperms, 

 are formed from temporary masses of cells (ovaries or testes], 

 which are developed towards the breeding season by a pro- 



n> 



FIG. 112. Nereis. Anterior portion of nervous system, comprising the brain, the 

 oesophageal connectives, and the anterior part of the ventral nerve-cord. .(After 

 Quatrefages.) 



liferation of the cells of the membrane (peritoneum) lining 

 the coelom and the structures it contains. 



Ova and sperms, when fully ripe, are discharged, reaching 



