N0TK8 OX THE H [S'lTUOBDELLID.E. 
213 
Thk Nephkidta. 
There are three pairs of nephridia (Text-fig. 1) in both 
male and female. The nephridia of the first pair (head 
nephridia) are alike in both sexes. Each begins in the 
lateral part of the neck segment, not far from the lateral 
border. In some series of sections each tube seems to have 
its origin in a thin-walled vesicle. From its point of origin 
the nephridial tube runs inwards with a curve, the con- 
vexity of which is directed backwards, and crosses the 
middle line, running ventral to the oesophagus and some 
little distance behind the posterior extremities of the jaws. 
After crossing the middle line the nephridium extends for 
a little distance further in the same direction, and then bends 
sharply round on itself, forming a complete loop, and running 
back almost parallel with and somewhat in front of its 
first-mentioned inwardly trending limb, till it reaches a point 
not far from the origin of the latter, when it again changes 
its course to run straight forward into the head. In the 
head the nephridium is traceable by means of its contained 
cilia to a point nearly opposite the middle of the base of 
the anterior limb, where the ciliary movement is always 
found to cease in a position far removed from either surface 
of the head. In sections the tube is traceable to a point 
just in front of the cephalic limb, where it comes close to 
the ventral surface and terminates the!-e. It is at this 
point doubtless that the external aperture is situated. 
But apparently in this terminal non-ciliated part of the 
nephridium the lumen becomes divided up into a number 
of extremely minute channels, of which the openings on 
the surface would not be traceable. The wall of this 
nephridium is very delicate throughout, and it is in few series 
of sections that the arrangement can be followed. Where 
the loops overlap, on the ventral aspect of the neck-segment, 
the nephridia have the appearance of narrow channels lined 
by cilia running* through a mass of fibrillated material, in 
which a nucleus is embedded here and there. 
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