25O ELLIOT ROWLAND DOWNING. 



redii and the first of A. cristata return blood to the dorsal 

 vessel." On a priori grounds, it would be strange to find the 

 homologous blood vessels in closely related species carrying blood 

 in opposite directions. I am certain that in A. cristata the blood 

 flows from the dorsal vessel out to the parietal, the nephridial 

 longitudinal vessel and to the nephridium, in this branch of the 

 dorsal vessel. In this species the individuals are so large that in 

 chloretonized specimens the direction of the blood movement is 

 seen with comparative ease. S. E. Keith who has worked care- 

 fully for some time on the circulation of A. cristata gives me per- 

 mission to quote her on this point as follows : " I have referred 

 to these blood vessels in my own notes as the third pair of 

 branches of the dorsal vessel. Gamble and Ashworth speak of 

 the dorsal as receiving these branches, but the blood flows out- 

 ward in them I am sure." 



I have watched the blood-flow in A. Claparcdii ; the skin is 

 frequently so transparent it may be seen without dissection. The 

 flow is certainly away from the dorsal vessel in this species also. 

 I am reasonably certain that such is the case in A. marina, in 

 chloretonized specimens of which I have watched the blood 

 movement. In this opinion I am supported by Willem who says 

 of marina, " II faut remarquer de plus, au point fonctionnel, que 

 le sang circulant dans le tronc dorsal d'arriere en avant, le contenu 

 des trois branches qui en emanent progresse dans une direction 

 centrifuge." 



Lillie makes the statement that " The vessel (segmental) begins 

 its formation at the junction with the subintestinal blood vessel. 

 Near its junction with the body wall the main vessel (segmental) 

 gives off a branch (the nephrostomial vessel) which curves back, 

 passes inward and barkward along the dorsal lip of the nephros- 

 tome." From this quotation it is evident that Lillie traces the 

 afferent nephridial vessel to the subintestinal blood vessel, while, 

 as stated above, I trace it, in agreement with Gamble and Ash- 

 worth and other observers, to the ventral vessel. The contra- 

 diction is only verbal, not real, for Lillie, in the explanation of 

 his figures, labels this subintestinal vessel " the subintestinal or 

 ventral vessel," a usage which he gets from oligochaet anatomy 

 and which is incorrect here. Lillie finds that in Arenicola as in 



