FORM OF NEPHRIDIA IN ARENICOLID^. 249 



ent vessel gives off no branches to the nephridia, but the latter 

 are supplied by a branch from the parietal. 



The branch of the dorsal vessel to the second nephridium is 

 small in A. Claparedii, but functional still. Gamble and Ash- 

 worth show and describe an afferent vessel to the first nephridium 

 of A. marina ; with this V. Willem disagrees, showing for this 

 nephridium only a branch from the dorsal. In the majority of 

 cases I find a branch from the ventral vessel .also, thus agreeing 

 with Gamble and Ash worth ; in a few animals it is apparently 

 wanting. I do not find, however, the efferent vessel from the 

 fourth nephridium, in A. marina, to the subintestinal, which 

 Gamble and Ashworth show but which V. Willem claimed was not 

 present. 



It is not true that the three main branches of the afferent vessel 

 break up into capillaries ; the one to the setal sac and gill does. The 

 one to the integumentary vessels unites with them. The branch 

 which enters the funnel continues as the gonadial vessel, runs 

 peripherad to the nephridium and connects with the nephridial 

 longitudinal, except in A. Claparedii. 



The parietal and nephridial longitudinal vessels are distinct 

 throughout the nephridial region in A. GmbH, A. ecaudata and A. 

 marina. In A. cristata, the parietal is distinct but the nephrid- 

 ial longitudinal, while large at the level of the first nephridium, 

 tapers posteriorly, becoming obscure back of the third nephridium. 

 The parietal vessel is distinct the entire length of the nephridial 

 region in A. Claparedii. The statement of Gamble and Ashworth 

 that it is absent in this form is only explicable because they 

 worked on preserved material ; it is plainly evident in the living 

 worm. The nephridial longitudinal, as a distinct vessel, is ab- 

 sent in this form except in the region of the first nephridium: its 

 place is taken by a series of small connecting vessels, as if the 

 gonadial vessel branched and some of its branches ran back to 

 connect with those of the next posterior gonadial vessel. 



In all cases the branches of the dorsal vessel running to the 

 nephridia are afferent vessels. Gamble and Ashworth state that 

 " The first nephridia of A. Grubii and A. ecaudata are supplied 

 by a branch from the dorsal vessel " (the italics are mine), yet 

 " The first three nephridia of A. marina, the first two of A. Clapa- 



