192 MR. A. HANCOCK ON THE ANATOMY OF DORIDOPSIS. 
diagonally backwards, is once more attenuated and sinks into the anterior surface of the 
liver on its way to the true stomach, which is buried in that viseus. The cesophagus, 
which is considerably longer than the proboscis, has it walls somewhat follieulated, and 
forms a sort of crop or anterior stomach (Pl. XVII. fig. 2m), which has its mucous mem. 
brane thrown into numerous wrinkles, giving to the surface a honeycombed appearance, 
The stomach (Pl. XVI. fig. 2) is rather large, lies in the centre of the liver, and partakes 
considerably of the form of that organ, being rounded in front and bilobed behind. lis 
inner surface presents numerous large irregular depressions, within which are many smaller 
depressions (g) divided by elevated ridges, giving to the whole a eoarsely reticulated 
appearance. There can be little doubt that these depressions, large and small, are the 
biliary ducts, which have lost their tubular character, and are reduced to mere openings 
or depressions in the substance of theliver. Be this, however, as it may, there are no 
distinct channels or ducts, properly so called, for the passage of the hepatie secretion; 
and it is evident enough that the bile must enter the stomach through the cell-like 
depressions that everywhere exist in its walls. Indeed the stomach may be looked 
upon as a much-folliculated sac with the hepatic matter suffused over the surface, and 
giving its secretion everywhere through the walls of the follicles. Here, then, we 
have à very interesting modification of the hepatic organ; for we see in it, in this 
instance, an intermediate step in development between the complete specialization 
of the organ in the Doridide and the more or less fusion of it with the stomach in 
the Holidide. 
A very delicate mucous membrane may be traced, in minute folds, on the ridges that 
separate the cells in the gastrie wall. 
The liver (Pl. XVII. fig. 1 m) is of a brownish-yellow colour ; it is large and elongated, 
with the anterior margin enlarged a little, rounded, and slightly hollowed. Behind, it i 
cleft for some distance into two lateral lobes (n), which pass backwards, one on each side 
of the branchial circle. 
The intestine (0) issues from the dorsal wall of the stomach a little behind the cso- 
phagus, and penetrates through the upper surface of the liver. Itis rather dilated at 
the pyloric extremity (Pl. XV. fig. 12), and, turning forwards and to the right, it almost 
immediately doubles upon itself, and then, taking a backward course, passes under ue 
pericardium, and soon terminates at the anal nipple, situated in the centre of the branchial 
circle. Its walls are rather delicate, the muscular layer being thinner than usual, and 
the mucous membrane not by any means strong. The latter rises into delicate — 
tudinal folds, which are best defined in the dilated portion near to the pylorie extremity, 
Where there is one fold, very much larger than the rest, that is continued into the stomach 
(Pl. XVI. fig. 2f). 
The alimentary system of D. nigra (Pls. XV. & XVI. figs. 2 & 1) varies very slightly from 
that of D. gemmacea. The dilated portion behind the proboscis is scarcely distinguish- 
able, as it is only a very little wider than the proboscis itself. The crop or anterior 
stomach is well developed, and the constriction before and behind marks it off with 
great emphasis. The mucous membrane of the latter (Pl. XX. fig. 1e) is wrinkled much 
in the same manner as it is in D, gemmacea; and the proboscis (5) is quite smooth 
