168 
shaped cells of the excretory portion of the nephridium, 
which, even in young specimens, contain some excretory 
granules. Sections of the nephridia of young specimens 
show that the cells hning this part of the organ bear one 
or two long cilia on their inner ends, and that thei some- 
what vacuolated protoplasm contains comparatively few 
concretions (fig. 30). In older specimens the concre- 
tions in the cells are very numerous, filling up the middle 
and part of the distal region of the cell. The granules 
are either black or yellowish, and some at least consist 
of acid-urate of sodium (Willem). The distal fourth of 
the cell is almost free from granules; they appear to have 
been extruded into the cavity of the nephridium. Con- 
siderable collections of such yellow granules are 
occasionally found in the lumen of the organ. Finely 
powdered carmine, when injected into the coelom, is taken 
up by the cells lining the excretory portion of the nephri- 
dium, and afterwards extruded in small masses. Below 
the excretory epithelium there is a thin, almost structure- 
less, layer of connective tissue, while in the walls of the 
vesicle there is a thin layer of muscle fibres. in a corre- 
sponding position. In young specimens the cells lining 
the vesicle contain fewer granules than those of the 
middle part of the nephridium; but in old specimens 
there is little difference in this respect between the cells 
of the two regions. 
The network of blood-vessels with which the nephri- 
dium is provided les between the excreting epithelium 
and the thin celomic epithelium which covers the organ. 
From the dorsal vessel a branch is given off which 
runs on the anterior face of the first diaphragm. This 
divides—one part supplies the body wall in the region of 
the third setal sac, and is there connected with the longi- 
tudinal dorsal vessel; the other part enters the funnel of 
