592 DR. R. V. ERLANGER. 
end of the mucous gland (muc.), and the mantle cavity (M.). 
To the left lies the left kidney (M.) which is considerably 
smaller than the right one (Nr.), of which a part can be seen 
on the right side of the pericardium. All these organs are 
viewed by transparency through the mantle. In order to dis- 
play the external openings of the kidneys, it is necessary to 
lay open the mantle cavity and to turn back the rectum, which 
is dorsally attached to the mucous gland. A dissection of 
this kind is figured in fig. 2, where both nipples are to be seen 
(X/. and Xr.) at the base of either ctenidium (B/. and Br.), and 
to either side of the rectum (R). The right ctenidium (Br.) 
is about a fifth smaller than the left. This fact has already 
been mentioned elsewhere, but I desire to lay special stress on 
it, as it will be made use of in the comparative part of this 
paper. 
The right kidney is a large gland, the shape and relations 
of which have been accurately described by Wegmann (27), 
while Perrier (23) has ably figured its histological structure. 
Having no intention of entering into histological detail I 
simply refer the reader to Perrier’s memoir on this subject. 
The left kidney has the shape, and in large specimens the 
size of a hazel-nut; the numerous papillze which it contains 
give it externally a velvety appearance (Wegmann). 
When the pericardium has been dissected out, opened 
transversely from behind and the heart (ventricle and both 
auricles) removed, the opening of the left reno-pericardiac 
duct into the pericardium can be easily seen (fig. 3, Y) ; it is 
situated to the left of the rectum, and lies between this and 
the left auricle. This is shown in a frontal section (fig. 9). 
The reno-pericardiac duct is, as Perrier has already stated, a 
canal of no inconsiderable length, and its presence can be 
readily detected in frontal sections, while, on account of its 
direction, it is somewhat more difficult to trace in transverse 
sections. There is no proper genital duct in Haliotis, and the 
gonad communicates with the right kidney by aslit-like open- 
ing, which, according to Perrier (28), has a special valve 
closed in all times except in that of sexual maturity. 
