NERILLA AN ARCH I ANNELID. 
409 
mid-ventral groove (figs. 9, 10, 15). Inwards from the pore 
passes the tube coiled in a single twist and forming a swollen 
body lying at the base of the parapodium. Springing from 
this body a post-septal canal runs straight to the septum in 
front, through which it opens into the next segment by the 
funnel. 
Structural details can best be seen in the second neph- 
ridium, which is the longest and best developed of the series 
(fig-. 16). The small, but widely open funnel bears on its 
outer and lower lip a number of extremely long cilia, which 
work down the canal. A few similar long cilia are attached 
to the wall of the nephridial canal further down its course. 
The wall of the post-septal canal is formed of finely granular 
cells at first, but as it nears the coiled region the wall 
thickens, and large vacuoles appear in it (figs. 16, 17). These 
vacuoles soon reach a great size ; they are present through- 
out the coiled region, disappearing again near the nephri- 
diopore. Each is filled with a clear liquid, in the centre of 
which is suspended a large, very highly refringent granule, 
constantly agitated with the Brownian movement. Both the 
granule and the liquid are probably of an excretory nature, 
and are, I believe, discharged into the lumen of the neph- 
ridium. Very conspicuous in the living worm, these granules 
were noticed long ago by Claparede (3). No cell outlines are 
visible in the nephridium ; in sections the vacuoles are seen 
to be much more numerous than the rare nuclei (fig. 36). 
The lumen is almost certainly intra-cellular. 
The first nephridium is rather smaller than the second, but 
scarcely differs from it in structure. On the other hand the 
third in the female generally appears of looser texture, with 
less regularly disposed vacuoles, and a wider lumen some- 
times irregularly distended at intervals. It is a little smaller 
than the second, but larger then the first. By far the 
smallest nephridium is the last, in the ninth segment of the 
male and in the eighth segment of the female. The lumen of 
this nephridium is less coiled and is often greatly distended 
(fig- 15). 
