282 LOUISE HOYT GREGORY. 



where it unites with a large ciliated organ in the next anterior 

 segment. (This union is shown in Figs. 2 and 3.) The walls of 

 the nephridium are thin, its cells contain numerous excretory 

 particles and its cavity is lined with fine cilia. The organ re- 

 ceives its blood supply from branches of a ventral longitudinal 

 blood vessel. The position of the blood vessel is shown in the 

 sagittal section, Fig. 2. The organ as a whole is simple in struc- 

 ture and may be regarded as a more or less degenerate condition 

 of the nephridium as seen in Hesione pantherina, the nephrostome 

 in the latter being replaced by the ciliated organ. 



Fig. 2. X 5°°- A sagittal section of the segmental organ. Showing the relation- 

 ship between the ciliated organ and nephridium. C. O, ciliated organ ; S, septum ; 

 N, nephridium ; B. V, blood vessel. 



The ciliated organs of Podarke, like the nephridia, are paired 

 in every segment behind the pharynx. The organ is a thin, fiat, 

 more or less triangular plate of ciliated cells, one layer in thick- 

 ness, which stretches out into the body cavity anteriorly away 

 from the dissepiment with the distal edge of the organ, or the 

 base of the triangle turned toward the intestine and the apex of 

 the triangular mass attached to the nephridium. The dorsal edge 

 of the fiat plate is rolled over toward the dissepiment. At the 

 posterior edge it is often compressed and folded, but gradually 

 broadens out into a large lip at the distal end. The ventral por- 

 tion is only slightly rolled and in this case the turn is away from 



