THE NEPHRIDIA OF THE POLYCHiETA. 711 



At the level of the septum the excretory products cease to 

 appear, the tube becomes narrower, and then enlarges again 

 as it passes into the funnel. The nephrostome is here also 

 provided with a long lower lip, to which is attached a bunch 

 of long powerful cilia. There is shown a short upper lip 

 without cilia; but this may possibly be only the edge of the 

 lower lip seen in optical section, since I was unable to find it 

 in sections (fig. 85). It will be seen, then, that at this stage 

 the funnel of the nephridium has all the appearance of being 

 a true nephrostome — the open extremity of the nephridial 

 tube, continuous with it, and of the same substance. It 

 bears a strong resemblance to the nephrostomes of the 

 smaller Oligochgetes, such as Bnchytraeus (9). 



If we now examine the structure of the excretory organ in 

 a fertile and genitally mature segment of a Syllid, we shall 

 find a very different state of things (figs. 20 and 38). 



Sections of the mature organ show that the lumen of the 

 canal is somewhat enlarged, and often much distended with 

 genital products, but that its walls are otherwise little 

 changed in appearance, whilst in front of the septum, in 

 place of the little nephrostome, a large ciliated funnel has 

 become developed. The lip runs high up on the anterior 

 face of the septum, then curves round to meet below in a 

 projecting shorter lower lip. The funnel forms a large 

 trumpet-like opening to the nephridium, and its walls extend, 

 as those of genital funnels generally do, partly on to the 

 septum, and partly on to the body-wall (figs. 21 and 38). 

 The histological structure of this richly ciliated newly deve- 

 loped funnel is quite different from that of the true ne- 

 phridium — resembling, in fact, that of the genital funnels 

 described in the Phyllodocida) above ; and it is sharply marked 

 off from the nephridium at the point where the nephrostome 

 was previously situated (fig. 30). The nephrostome can no 

 longer be distinguished. The little mass of cells described 

 above (fig. 37) as situated over the projecting lower lip of 

 the nephrostome, must be regarded as the rudiment of the 

 genital funnel, strictly comparable to the rudiments shown 



