NEEVOTJS SYSTEM. 



371 



breeding season as oviducts or vasa deferent ia, and permit of the 

 passage outwards of the generative products, which have been set free 

 in the bodi/ cavity. 



Amongst the special glands in the body of the Clitetopoda, those 

 cutaneous glands of the OUgochceta which give rise to the thickening 

 (extending over several segments) known as the clitellus or girdle, 

 are especially worthy of remark. The secretion of these glands 

 perhaps assists the intimate connection of the Worms during copula- 

 tion. In the 8erpulidce there are present two large glands, which 

 open upon the dorsal surface of the anterior portion of the body and 

 furnish a secretion used in the formation of the tubes in which the 

 animals live. 



a 



FIG. 301. Brain and anterior portion of the ganglionic chain, a, of ScrpiiJa 5, of Nereis, 

 (after Quatrefages) ; O, eyes ; ff, cerebral ganglion ; c, cesophageal commissure ; Ug, 

 suboesophageal ganglion; e e, nerves to the tentacular cirri and the mouth segment. 



Nervous system. The longitudinal trunks of the ventral cord are 

 often so closely approached that they seem to form a single cord 

 (Oligochreta}. In the Tubicolce (fig. 301), on the contrary, they are 

 very widely separated from one another, especially in the anterior 

 part of the ganglionic chain (Serpula). The visceral nervous system 

 consists of paired and unpaired ganglia, which supply the oral region 

 and especially the protrusible proboscis. 



Sense organs. Paired eyes upon the surface of the frontal (i.e, 



