74 ALFEED GIBBS BOURNE. 



blood-current in the dorsal vessel, and the downward direction 

 of that in the hearts. 



Of the blood which is brought forwards to the cephalised 

 region in the dorsal vessel the greater portion goes into the 

 hearts. Further, some or all of the blood going to some of the 

 hearts may be derived from the supra-intestinal vessels — some 

 in worms possessing both lateral and latero-intestinal hearts, 

 all in worms possessing both lateral and intestinal hearts ; the 

 other and most anterior hearts receive all their blood from the 

 dorsal vessel. 



When we come to the questions — 1. Whence comes the 

 blood into the dorsal vessel ? 2. Does any blood leave the 

 dorsal vessel other than in the cephalised region? — we find 

 great difference of opinion. There is in Megascolex, and pro- 

 bably in other worms, no great inflow at the posterior ex- 

 tremity ; and when the dorsal vessel is filling, it fills simul- 

 taneously along the greater part of its length. According to 

 Perrier (9, p. 504) and Benham (4, p. 255), blood enters the 

 dorsal vessel from what I term the dorso-tegumentary vessels. 

 I do not believe this to be the case. Vejdovsky (15, p. 115) 

 states, though without giving any reason, that the blood flows 

 from the intestinal capillaries into the dorsal vessel, and in this 

 I agree with him. 



The problem may be stated as follows : 



A large quantity of blood leaves the dorsal vessel in the 

 cephalised region. In some worms some of that blood may 

 come to the dorsal vessel, in that region, from the supra- 

 intestinal vessels, i. e. from the intestinal capillaries ; but what 

 we want to determine is, does any of it come in all worms 

 from branches connected with the dorsal vessel in the posterior 

 regions of the body ? The vessels which are so connected seem 

 always to be of two kinds, dorso-tegumentary vessels and dorso- 

 intestinal vessels ; and there can be, I think, no doubt that, in 

 order to constantly replenish the dorsal vessel along its whole 

 length, blood must come from one of these two kinds of 

 vessels. Does it come from both kinds, or only from one? 

 If the latter, from which ? I thii)k from the dorso-intestinal 



