FORM OF NEPHKIDIA IN AREN1COLID/E. 



247 



nephridium, divides, one branch going to the setal sac and gill, 

 if present, one to the integumentary vessels and one to the 

 nephridium. The latter enters the nephrostome and forks, one 

 branch traversing each lip. After reuniting, the vessel, reformed, 

 runs out onto the wall of the nephridium as the gonadial vessel. 

 Each of the three main branches of the afferent vessel gives off 

 smaller vessels which, with more or less anastomosing with ad- 

 jacent vessels, form capillary net-works in the organs supplied. 



FlG. I. Partly diagrammatic cross-section of Arenicola cristata at about the level 

 of the first nephridium. D.V., dorsal blood vessel. H., heart. L.G.T., lateral 

 gastric blood vessel. N., neural blood vessel. N.L. V., nephridial longitudinal 

 blood vessel. P., parietal blood vessel. S. V., sub-intestinal blood vessel. V. t 

 ventral blood vessel. 



The efferent vessels are formed by the union of capillaries in these 

 same regions. 



The afferent vessel, as a rule, comes from the ventral vessel. 

 This is true for all except the first two nephridia of A. Grnbii and 

 of A. ecaudata, which nephridia are supplied, the first by a branch 

 of the dorsal, the second by a branch of the parietal vessel (Fig. 

 2, c/). In addition to the afferent vessel from the ventral vessel, 

 the following nephridia also receive branches from the dorsal 

 vessel : the first of A. cristata, the first two of A. Claparedii and 

 the first three of A. marina (Fig. 2). 



The following nephridia return blood directly to the subintes- 

 tinal vessels through efferent vessels whose numerous branches are 

 adjacent to theirfunnels : the fourth, fifth and sixth of A. cristata, 

 the fourth and fifth of A. Claparedii and the fifth and sixth of A. 

 marina. All others must pour the blood into the parietal and 

 nephridial longitudinal vessels which, in turn, pass it to some of 

 the more posterior efferent vessels (Fig. 2). 



