776 CONTRIBUTION TO AUSTRALASIAN OLIGOCH^TA, I., 



segments vii.-x., and Benham describes pregenital nephridia as 

 being present in segments vii. and x. in P. lacustris. 



Nervous system. — The brain lies in the cavity of the buccal 

 segment in close apposition with the antero-dorsal wall of the 

 pharynx, being directed obliquely so that its ventral portion 

 projects slightly into the prostomium. It is in the form of a 

 biconvex mass, the anterior boundary being strongly convex, the 

 posterior surface only slightly so. From the ventral extremity 

 there pass round the buccal chamber, on each side, two stout 

 strands of neural material — the oesophageal connectives — which 

 unite in the second segment to form, together with the mass of 

 nerve-cells, the subcesophageal ganglia of the ventral nerve-cord. 

 These connectives of neural cords lie in close apposition with the 

 anterior wall of the pharynx, enclosing between them the narrow 

 buccal cavity; and each is accompanied by one of the blood- 

 vessels formed by the bifurcation of the dorsal vessel. A massive 

 structure containing an abundance of nerve-cells arises from the 

 posterior surface of the brain, and projects into the cavity of the 

 pharynx, as mentioned previously. Neurocordal substance is 

 sent off, in the form of two strands, to supply the prostomium 

 and what corresponds to an upper lip. 



Reproductive system. — Male organs: the testes are paired 

 structures attached to the anterior wall of segment xi. The 

 cavity of this segment is filled with a mass of developing sperma- 

 tozoa formed by the breaking up of the testes. This mass consists 

 of ripe spermatozoa together with aggregations of rounded cells 

 representing developing spermatozoa, and resembling closely 

 similar aggregations in the Encliytrceidce. Outside this segment 

 no spermatozoa are visible. In an examination by transmitted 

 light of an entire individual, this mass of spermatozoa is very 

 evident as giving rise to an opacity which occupies a great part 

 of the body-cavity lying dorsal and lateral to the digestive tube, 

 which is thereby displaced towards the ventral body-wall, and 

 practically surrounded by the mass, except on the ventral aspect. 

 Among this mass of developing spermatozoa are pear-shaped 

 bodies, probably sporozoaC?). 



