Contributions to a Knoivledge of South African Hirudinea. 253 
Lastly, in specimens in which segmenting ova are present in the pouch, 
the ventral aperture of the pouch is closed, so that no other method of 
fertilisation seems possible. The sole function of the pore is to allow of 
the escape of the young. 
Nervous System. — The course of this system will be readily understood 
from the diagrams. It passes backwards in the ventral median line as 
far as somite xv, and then ascends immediately in front of the anterior 
wall of the brood pouch to the dorsal side, between the two anterior 
horns of the brood pouch. 
Transverse sections through the brood pouch region show the nerve 
cord in a median triangular projection of the dorsal body substance into 
the brood pouch. 
The cord descends again behind the brood pouch, in close association 
with the posterior wall of the latter. 
