STUDIES ON EARTHWORMS. 257 
In Urocheta the first pair of nephridia are much modified 
and consist of a rosette of tubules opening into a large vesicle, 
and closely applied to the pharynx. 
[The greatest development seems to take place in Micro- 
cheta, where all the nephridia have the structure of the first 
nephridium of Urocheta, but have an immense vesicular 
region. Other Earthworms, that I shall describe later, also 
have large elongated vesicles, and comparatively short glan- 
dular region. ] 
In Pontodrilus the anterior nephridia seem to be simple 
tubes, but in those posterior to the genital organs an immense 
compact glandular region is added, whilst the free portion of 
tubule is short. 
In Moniligaster the nephridia are rather smaller in the 
genital somites than elsewhere. 
As to the pores of the nephridia, the position of which 
relative to the sete is an important generic character, we 
have more information, 
Kinberg, as a rule, makes no mention of them, but in 
describing Geogenia he says the “ lateral pores ” are in a line 
with the dorsal setz. 
I have already mentioned the position of these pores in the 
various genera in describing the external features. As a rule, 
they are placed in the anterior region of the somites, just in 
front and slightly dorsad of either seta 4 or seta 2 (the upper 
seta of the lateral or of the ventral couple). Butin Urocheta 
they are in this relation to seta 3 (the lower seta of the lateral 
couple), whilst in Plutellus they alternate between setzw 4 
and 2, and the first five are in line with seta 3. 
In a species of Acanthodrilus from New Zealand, Beddard 
has described (42) the position of the nephridia as alternating 
from somite to somite with the two couples of setz ; coinciding 
in one somite with the lateral, in the next with the ventral, and 
again, in the succeeding somite with the lateral couple of setz. 
Moreover, these two sets of nephridia are different from one 
another; the ventral nephridium has a large diverticulum, 
whilst the dorsal one has a very small diverticulum. This fact, 
