96 Olive B. Davies : 



absent in the more anterior ones. From 'this backwards there 

 appears to be a pair in each segment, except in those segments 

 across which future fission takes place. Here it would be hard to 

 distinguish them if they were present, owing to the thickening of 

 the body wall, and the outgrowths from the ventral nerve cord. 



The openings of the nephridia to the exterior are situated imme- 

 diately in front of the bundles of setae of the same segment; follow- 

 ing back from this opening is a dilatation, and back from this 

 a much coiled tube ending in a large swelling. (Fig. vii. B.) 



Nervous System. 



The nervous system consists of a dorsal bilobed cerebral ganglion 

 (Fig. iii. C.G.); from this two stout commissures run down either 

 side of the pharynx, and from a bilobed ventral ganglion (Fig. iii. 

 A.V.G.); from this the ventral nerve cord (Fig. iii. N.C.) runs down,, 

 with typically a ganglion in each segment; but in the anterior seg- 

 ments the ganglia are somewhat irregular, and the nerve cord and 

 ganglia are double. This is clearly seen in Fig. iii. 



Reproductive System. 



I could not discover a trace of reproductive organs in any specimen 

 I examined. The animal reproduces asexually by fission ; but it 

 seems to be a much slower process than in C. austrolis. Also' 

 secondary fission before primary is complete seems to be the rule 

 in this species. (Fig. ii. L.F.2.) 



It is doubtful whether these species of Chaetogaster are truly 

 parasitic. In some individuals small crustaceans were found in the 

 alimentary canal, but in others it Avas almost empty. The fact that 

 specimens were found in the pulmonary chamber also indicates that 

 there may be another mode of nutrition. It certainly seemed tcv 

 cause the death of a great many snails in my vessels; but this may 

 have been due to suffcation by the blocking up of the pulmonary 

 chamber and its opening by the worms. Some of the European 

 species are said to be internal parasites, but most others seem to use 

 the snail more as a means of progression and as a shelter. 



(J. australis appears to most resemble G. hengalensis. It differs 

 from it in the number of its setae in each bundle, and their 

 different arrangement; in its much smaller size and in several minor 

 characteristics; C austratis also has a preference for crawling right 

 into the pulmonary chamber of the snail rather than staying oi> 

 the outside. 



