116 
E. S. GOODRICH. 
that tlie blind iutevnal extremities are provided with soleno- 
cyte tubes. 
The stiff refringent solenocyte-tubes run free from the 
protoplasm of the umbrella-like web, and are attached to it 
only at one end, which may be called the outer end. The 
opposite end of the tube plunges though the wall of the 
nephridial canal, into which it opens. The flagellum passing 
down the tube into the nephridial lumen is of remarkable 
length. Thickened protoplasmic ridges pass radially along 
the web from the central mass to the periphery, where they 
embrace the outer extremities of the tubes. The apparatus 
may be either expanded or contracted, as can be seen in the 
figure. In the expanded condition the web is flattened out with 
the tubes widely diverging; the central mass and contained 
single nucleus then lies somewhat flattened in the middle. 
When the web closes up, the tubes are on the contrary drawn 
together until they become almost parallel, and the central mass 
with its nucleus is made to bulge outwards as a convex knob. 
There is no doubt, then, that in P. neapolitanus a single 
nucleus, at the tip of each branch of the nephridial canal, con- 
trols a set of from six to seven solenocyte tubes. If Woltereck’s 
recent description of the nephridium of a North-sea larva is 
correct, it would appear to differ considerably in structiu’e ; for 
he states that there is a nucleus to each tube, that the tubes are 
covered by the cytoplasm, and figures no web between them 
(16). In an important paper on the development of Poly- 
gordius. Shearer (15) has given a most careful account of the 
origin of the larval nephridia ; they arise from two cells 
differentiated quite early, lying on the inner surface of the 
ectoderm, and probably derived from it. Each of these cells 
multiplies to form a chain which develops into the whole 
nephridium. T'he solenocytes arise from the extremity of 
the nephridium itself. These observations entirely confirm 
the view that the canal and solenocytes of the Annelid 
nephridium form a whole, a single organ derived from one 
rudiment, strictly comparable to the canal and flame-cells of 
the platyhelminth excretory organ. 
May 12th, IhOT 
