STRUCTURE OF UROOH^ETA AND DICHOGASTER. 271 
numerous) the tuft of tubules attached to the posterior wall 
was in communication through the septum with the nepliri- 
dium of the segment behind. This seems to me to indicate 
that the nephridial system of Deinodrilus is in a more 
archaic condition than that of either Acanthodrilus or 
Dichogaster. In Deinodrilus the primitive disposition 
of the excretory system ofPerichseta has been so far retained 
that there is still an intersegmental communication here and 
there. The metameric arrangement of the nephridial system 
is not so complete as in Acanthodrilus and Dichogaster, 
though, for the matter of that, neither of these forms have an 
excretory system perfectly metameric in its disposition. 
Another point of difference between the excretory system of 
Perichgeta on the one hand, and that of Acanthodrilus, 
Deinodrilus, and Dichogaster, is in the form of the ex- 
ternal orifices. 
Professor Spencer (28) described the external orifices of 
the nephridia of Megascolides in the following words: 
“ The external opening itself is formed of cells of the epidermis, 
so modified as to present very much the external appearance 
of a taste-bulb ; that is, they form a sphere with the cells 
thicker in their middle parts, and the two ends attached to the 
poles of the sphere, the duct passing right up through the 
centre.” 
This description applies very closely to the modified epi- 
dermic cells which surround the nephridiopores ofPerichgeta. 
When I first observed these cells in Perichseta I thought for 
a moment that they really belonged to sense organs. The cells 
are so much swollen in their middle parts that the duct which 
forms up between them is of au excessively fine bore ; for this 
reason it is not always easy to detect upon fragments of the 
cuticle the actual orifice. 
