514. MR. A. HANCOCK ON THE STRUCTURE AND HOMOLOGIES OF THE 
In Doris tuberculata it is prolonged into a tube (Pl. LIV. fig. 2), which, turning for- 
wards, runs along the median line almost to the anterior extremity of the trunk-portion of 
the cavity, where it opens into it by a slit-like orifice. The tube overlies and partially 
conceals the great branchio-hepatic vein, and is liable to be confounded with its branches 
and with the divisions of the oviduct, which in certain conditions is also apparent 
through the floor of the renal chamber. It was by the complication produced by all 
these branches and by those before mentioned, which form a network in the walls of the 
chamber, that we were originally deceived into the belief that the tubular prolongation of 
the vesicle was itself branched, and was in this way connected with the liver. 
It is above stated that the vesicle seems to penetrate the wall of the renal chamber. 
It does not in fact do so, but passes between it and the liver, and bulges so; far into the 
cavity as to appear to have passed into it, especially as the floor of the chamber is so 
extremely delicate as to be scarcely, if at all, demonstrable. Hence it is that the vesicle 
and its tubular prolongation have the appearance of being adherent throughout to the 
floor of the organ. 
The wall of the tubular prolongation is delicate and glandular. The vesicle itself has 
a firm, compact appearance, and is generally of a brownish-yellow colour. It is supplied 
with muscular fibres, which stretch in all directions throughout its walls; and there is 
also a distinct belt of similar fibres surrounding the orifice opening into the so-called 
pericardium, which no doubt will act as a sphincter to guard this passage of communica- 
tion. The muscular belt was very distinctly observed in Tritonia Hombergii. The inner 
surface of the vesicle is strongly plicated longitudinally, the plieze being furnished with 
lateral laminae, and the whole so arranged in many cases around the orifice leading into 
the pericardial chamber as to act as a sort of valve to prevent fluid returning into the 
latter from the vesicle. The plice and their lamin are covered with large vibratile 
cilia, which are inclined from the orifice inwards, probably for the purpose of sweeping 
fluid from the so-called pericardium into the vesicle. Each cilium projects from the 
pointed extremity of an ovate vesicle, which is filled with minutely granular matter. 
The broad ends of the vesicles are crowded together and assume an hexagonal form, 
clothing everywhere the plice with a sort of pavement-epithelium (Pl. LIV. fig. 6 and 
Pl. LY. fig. 4). The ciliated epithelium is very deciduous, and can only be observed 
when the specimen is in a good state of preservation. It has been detected, however, in 
Doris tuberculata and in some other species. It occurred in a very perfect condition in 
Tritonia Hombergii, in which the cilia are unusually large, measuring about sooth of an 
inch in length. 
There is no remarkable difference in the character and arrangement of the pericardial 
chamber and the pyriform vesicle in D. bilamellata, D. repanda, and D. pilosa, except 
that in the first the glandular prolongation of the vesicle is continued quite to the ante- 
rior margin of the liver, where it terminates in an opening placed a little to the right 
side, and that in the last the prolongation is entirely deficient (Pl. LIV. fig. 3), the 
narrow extremity of the vesicle opening at once by a widish orifice into the renal chamber. 
This orifice is placed close to the floor of the chamber, so that it is overhung by the pro- 
Jecting wall of the vesicle; thus a sort of valve is. provided which will prevent any fluid 
