MESSRS. HANCOCK AND EMBLETON ON THE ANATOMY OF DORIS. 227 
gives off several offsets on both sides, and ends at the anterior border of the liver by 
dividing into several branches. The inner surface of the pyrifortn organ is, as 
Cuvier has pointed out, strongly plicated*; the plicae are arranged on an intricate 
plan, and so that they can act as a valvular apparatus to prevent the return of blood 
that has once passed through. The orifice is capable of being contracted like the 
mouth of a purse. This is the condition of the parts, as we have observed them, in 
D. tuberculata ; but we have not yet seen how the branches of this tube terminate. 
In D. repanda, however, in which, as in the other species we have examined, the 
same organ, and branched tube proceeding from it, exist, and in which the tube does 
not extend so far forward as the anterior border of the liver, the terminal branches 
are lost among a minute network of twigs from the left side of the aorta, which are 
found to dip through the ovarium into the liver. In JD. hilamellata also, we find that 
fresh light is thrown upon this curious apparatus The tube attached to the pyri- 
form organ or heart, after passing forwards for about half the length of the liver, 
giving off numerous twigs, resolves itself into a multitude of other small branches. 
All these offsets go to form a very complete and close network lying over the hepatic 
vein in a superficial depression, and extending from one end to the other of the liver- 
mass; the sides of this plexus are united to a similar arrangement of numerous 
hepatic branches from both sides of the aorta. These branches, in D. repanda%, are 
extremely numerous, and have a regular and very beautiful parallel arrangement; 
and the two lateral posterior branches in this species, as well as in D.pilosa and 
D. hilamellata, give off from their outer sides numerous much-ramified twigs. In 
these two species of Doris, therefore, the branches of the tube leading from the pyri- 
form organ inosculate and form a network with those of the aorta ; they therefore 
convey blood. This blood, coming as it does into the pericardium through the 
minute pores, already mentioned as existing on the floor of that organ and flowing- 
through the vesicle or heart attached to it from the visceral cavity and intervisceral 
sinuses, is evidently venous ; and our belief is that the vesicle of Cuvier is a ventricle, 
the office of which is to propel venous blood along its tube and branches, which are 
arterial in character, into the network formed by these branches and those of the 
aorta. This nevv apparatus then has a decidedly portal character. 
The blood which has gone through the above network is conveyed through the 
liver to the hepatic vein, and we have satisfied ourselves that there is no channel of 
communication between this vesicle or heart and the external orifice near the anus ; 
indeed, its office necessarily precludes the idea of such connection. The orifice near 
the anus is small, and leads into an extensive, more or less ramified cavity or sinus §, 
the trunk of which extends forwards along the upper surface and median line of the 
liver; its principal offsets follow the course of the chief arterial trunks, and appear 
to terminate on the surface of the liver. 
* Plate XVI. figs. 3, 4 and 5. 
i Plate XI. fig. 3. 
t Plate XII. fig. 5. 
§ Plate XI. figs. 1, 2 and 3 ; Plate XII. fig. 1 . 
