512 MR. A. HANCOCK ON THE STRUCTURE AND HOMOLOGIES OF THE 
also from the peculiar way in which the parts are arranged. Even now, after it has 
been clearly demonstrated that the pyriform vesicle is connected with the renal chamber, 
it is not always possible to determine the fact in the British species originally examined, 
namely, Doris tuberculata, D. repanda, D. pilosa, and D. bilamellata. 
The examination of a single individual of the genus Scyllæa put the matter right at 
once, which the closest investigation of at least a score of the above species had failed to 
do. Thus it is evident how desirable it is in all difficult matters of this nature to have 
recourse to a diversity of examples; for the point that may be most difficult to solve in 
one may be exceedingly easy in another. On retracting our opinion as to the nature of 
the pyriform vesicle, it must also be stated that Cuvier was the first to show that this 
vesicle really opens externally—an assertion which we originally controverted. He, how- 
ever, seems to have been unaware that it also opens into the so-called pericardium. 
In Doris tuberculata, D. repanda, D. pilosa, and D. bilamellata there is a large, more 
or less ramified chamber or sinus stretching along the dorsal surface of the liver-mass, 
and having the pericardium lying above it. This, which is the renal chamber proper, is 
circumscribed by a delicate membrane, distinctly demonstrable above but intimately 
united with the liver-capsule below ; and in all the species it opens externally by a small 
pore placed a little above and to the right of the anal nipple, and communicates with the 
pericardium through the instrumentality of the pyriform vesicle. 
In D. tuberculata this chamber is much ramified (Pl. LIV. figs. 1 & 2); the trunk is 
rather narrow and extends along the median line from end to end of the liver-mass; it | 
expands a little and reaches backwards to the region of the branchial circle, where its 
wall becomes firmly adherent tothe skin. In front the trunk bifurcates, a branch passing 
along the right and left margin of the liver. Several ramified branches extend from 
the sides of the chamber and spread over the surface of this organ. Two or three of 
these at each side are longer than the rest, and reach for a considerable way round it. 
ee are likewise a few small branches which seem to penetrate the substance of the 
ver. 
The aorta runs forward, adherent to the membranous roof of the right branch of the 
bifurcation, which is prolonged and accompanies the gastric artery to the stomach, where 
it ends (as do apparently, as far as they could be examined, all the other branches) ina 
blind sac. Other arterial trunks from the root of the aorta run in like manner along the 
roof of the left branch of the bifurcation and that of the several lateral ramifications, 
while two pass backward in connexion with the trunk of the organ. The great branchio- 
hepatic vein runs backward along the median line under the floor of the chamber, bulging 
into it, and receiving numerous branches right and left. Tt reaches beyond the posterior 
extremity of the liver and becomes isolated within the chamber, and is surrounded by à 
thick, spongy-looking, glandular tissue, which extends for some distance along the trunk, 
and pervades the whole of the posterior portion of the renal cavity. 
The renal chamber proper in Doris repanda, D. pilosa, and D. bilamellata* is much 
* Figures of the renal chamber in these three sp 
of Doris," published in the 
is also given. 
ecies are given in the paper before alluded to, ** On the Anatomy 
‘Philosophical Transactions. The minute structure of the glandular lining of the organ 
