244 



J. Stephenson : Two Oligochste Worms. [Vol. I, 



The commissures lie at the sides of the buccal cavity and 

 unite below ; about one-third of their length from the cerebral 

 ganglion they each give off a branch which proceeds in a posterior 

 and dorsal direction, and curving inwards unites with its fellow 

 in a loop dorsal to the pharynx ; this loop shows two ganglionic 

 swellings, one on each side, which are very evident in text-fig. 6, 



* <:^» 



Fig 6. — Antprior part of nervous systern of C. f>plliicidus : hnrca.\ ganglia obvious, 

 buccal commissures imlistinct. ^Ketereiice letters as in Plates ix and x.) 



though the connecting strands were here scarcely discern'ble. The 

 fibres appear to enter the loop from the ventral portion of the 

 buccal commissure, not from the direction of the cerebral ganglion 

 {v. text-fig. 4 B and C). 



The ventral nerve-cord shows the longitudinal division into 

 two in its anterior portion, which is characteristic of the genus. 

 This is best seen when the animal is well extended ; the separation 

 between the halves then takes the form of elongated oval spaces 

 with bridges passing from side to side between them. In the much 

 more usual (under examination) somewhat contracted condition, 

 the longitudinal division of the cord is much less marked, and 

 appsars as a series of small circular buttonholes with puckered 

 margins (c/. text-figs. 4 A and 5 C) ; in this condition the outline of 

 the cord is irregularly nodulated. This longitudinal division extends 

 almost as far as the posterior end of the pharynx. 



The ganglia are placed in each segment after the fifth at the 

 level of the setal bundles. In the anterior part of the body they 

 are not clearly distinguishable, though on a lateral view a slight 

 thickening of the cord appears to exist anteriorly where it is formed 

 by the union of the commissures, and again just behind the 

 posterior limit of the pharynx. The first ganglion, however, that 

 is clearly recognisable is that of the sixth segment ; all are seen 

 better in a lateral view than in one from the ventral surface. 



The lateral expansions of the nerve-cord at the site of a future 

 division of the animal have been already referred to, and are illus- 



