190 EDWIN S. GOODRICH. 



converge towards the ventral and posterior extremity. The 

 edge of the ridges is extremely thin and jagged (figs. 19 and 

 26). The clear protoplasm of which it is formed contains a 

 number of fine refringent granules. 



Sections show that the organ is composed of the loose tissue 

 characteristic of these worms^ which has a fibrous appearance 

 when preserved (figs. 23, 24, and 25, c.o.). The nuclei are 

 scarce and scattered irregularly. 



In Nephthys the position of the ciliated organ is essentially 

 the same as in Hesione (figs. 7 and 8). Its upper expanded 

 portion rests on the same dorso-lateral vessel, d. I. v., and its 

 lower end forms a sort of deep groove or ventral prolongation, 

 V. proL, running down the body-wall near the intersegmental 

 groove. There appears to be no communication whatever with 

 the lumen of the nephridium. 



These ciliated organs occur in both sexes throughout the 

 body in every segment except about the first ten. They are 

 more fully developed in mature than in young specimens. 



The Nephridium. — The nephridium of Nephthys is of 

 very remarkable structure, representing, indeed, an entirely 

 new type of Chaetopod nephridium, unlike that of any 

 member of that group hitherto described. 



The small external aperture lies on the ventral surface of 

 the body below the parapodium, and a little beyond the outer 

 edge of the ventral longitudinal muscles. Leading from this 

 nephridiopore (fig. 8, neph, p.) is a narrow canal running 

 upwards, then obliquely forwards through the muscular 

 septum, at which point it becomes narrower still (at all events 

 in sections). Emerging from the septum the nephridial canal 

 runs inwards and forwards, clinging closely to a blood-vessel 

 from the body-wall which joins the ventro-lateral vessel. 

 Ascending the dorso-ventral vessel, and increasing slightly in 

 diameter, it passes along the inner and anterior edge of the 

 ciliated organ on the posterior non- ciliated surface. Finally it 

 emerges on the top of the ciliated organ, where it divides into 

 free branches forming a sort of plume. 



The structure of the minute nephridial tube is simple. The 



