BV T MAKVKV ,7UHNST0X. 53 



latter lie just above, and very slightly mcdianwards from, the 

 ventral vessels. In the region of the genital ducts, the ves- 

 sels become displaced, the dorsal stem becoming pushed 

 dorsally, and the ventral vessel ventrally, the sex-canals pas- 

 sing between them. At the extreme posterior edge of each 

 segment, the ventral vessels become connected by a narrow 

 transverse vessel. In the scolex and neck-region all four 

 trunks are of the same size. At abovit the level of the 

 middle of the suckers, the pair of vessels on each side form a 

 loop (Fig.l). No connection between the loops on opposite 

 sides could be detected in the specimen. 



(Jenitdlid. — The genital papilla is located laterally, in an 

 irregularly alternating manner, near the anterior margin of 

 each segment. It is usually not very prominent. The genital 

 pore is a rather large circular opening, which leads into a 

 spacious genital cloaca, whose wall contains a relatively large 

 amount of radiating and circular muscular fibres, the latter 

 evidently acting as a sphincter. This common genital 

 chamber may extend inwards for a distance of 0-10 mm., its 

 greatest width reaching 005 mm. Its usual form may be 

 seen in Fig. 9. At times the whole organ may be much more 

 elongate and distinctly tubiilar, probably as a result of the 

 action of the muscles in its walls (Fig. 10). The length then 

 may reach 0117 mm. but the lumen becomes very narrow, 

 being only 0-007 mm. Opening into the inner end of the 

 cloaca, one may readily recognise the male and female aper- 

 tures, the former lying immediately in front of the latter, 

 both being placed at about the same dorso- ventral level. 

 Occasionally the female pore is slightly more dorsally 

 situated. The male opening faces postero-Iaterally, and the 

 female antero-laterally, the two thus lying very close, and in 

 such a position as would suggest the probability of self-im- 

 pregnation in each segment, an event which was seen fre- 

 quently in the mature parts of the chain (Fig. 10). Both 

 pores not infrequently lie just between the excretory vessels, 

 though their usual position is just laterally to them. 



