CONTRIBUTIONS TO THE ANATOMY OF THE HIRUDINEA. 471 



The dorsal sinus communicates directly with the ventral 

 sinus only at its posterior extremity^ as described above. 



No branches are supplied to the crop, but considerable 

 branches are given off at intervals — two in each somite, in the 

 region where they exist, thirty-two pairs in all — and passing 

 through the botryoidal tissue terminate by anastomosing with 

 the superficial cutaneous networks. 



Such is the complicated system of vascular spaces in 

 Hirudo. 



The anatomical relations described above, which possess the 

 greatest interest and importance for the solution of the problem : 

 How far are these spaces "coelomic" in nature? may be 

 summed up thus : 



The whole system of vessels and sinuses is in continuity. 



The lateral vessels communicate freely with one another 

 without the intervention of any capillary system ; 



They possess branches opening into botryoidal or other 

 capillary networks of the ''cutaneous" system; 



They also form nephridial capillaries, which are partly col- 

 lected again and carried to the capillaries of the " cutaneous" 

 system, and partly unite to form a vessel which is connected 

 with the perinephrostomial sinus ; 



Again, they form capillaries upon the intestinal wall. 



The dorsal sinus is directly connected with the ventral sinus. 



The dorsal and ventral sinuses also severally communicate 

 with — 



1. The cutaneous networks ; 



2. The capillary network upon the walls of the crop ; 



3. The capillaries upon the intestinal wall and upon its 



spiral valve ; 



4. The perinephrostomial sinuses. 



The botryoidal and other '' cutaneous " capillary networks, 

 which appear to be one and the same system, communicate, on 

 the one hand, with branches of the lateral vessel, and upon the 

 other with the extensions of the dorsal and ventral sinuses. 



