474 ALFRED GIBBS BOURNE. 



remains developed around the vas deferens in Pontobdella, but 

 around the testes there is an almost complete sinus as described 

 above. Taking these facts into consideration it seems to be 

 quite possible that we have in these perigenital spaces portions 

 of coelom shut off at a very early period and in the amoeboid 

 cells and colourless fluid — the primitive blood of Hirudo. 



Hsemopis, Hsemadipsa and Aulostoraa. 



I have little to add regarding the vascular system in these 

 genera to what has been already described in Hirudo. 



In Hsemopis, the dorsal sinus appears to be much less 

 developed than in Hirudo. 



In Aulostoma the dorsal sinus has ceased to exist. 



In Aulostoma (a fact which lends great support to the theory 

 enunciated above) the spaces surrounding the female gene- 

 rative organs contain a red fluid. 



Nephelis and Trocheta. 



These genera present some most important variations upon 

 the arrangement described in Hirudo. (See woodcut, fig. 5, 

 p. 456.) 



The lateral vessels and their branches, in so far as I have 

 traced them, present a very similar distribution. The ventral 

 sinus is exceedingly large but the dorsal sinus is entirely absent 

 (fig. 63). 



It is in the botryoidal tissue that we find the most remarkable 

 new development. 



The botryoidal tissue is arranged as in Hirudo in dorsal 

 and ventral longitudinal bands which communicate (those of the 

 one side with those of the other) much more freely than in the 

 former genus. 



The botryoidal tissue exhibits throughout the body a ten- 

 dency to acquire a very large lumen and appears to be capable 

 of great distension by blood. In the lateral regions of the 

 body occurs a metameric series (11 pairs) of dilatations of 

 botryoidal tissue (fig. 63, coel.). They only occur in the central 

 portion of the body, the most anterior pair being posterior to 

 the copulatory organs. 



