226 MESSRS. HANCOCK AND EMBLETON ON THE ANATOMY OF DORIS. 
of an internal or venous branchial circle* which closely surrounds the anus. The 
blood from this circle passes on to traverse the branchial leaflets or plumes, by run- 
ning up the inner side to the apex and then down the outer side to the base of the 
division, and then falls into a second, or external, or arterial circular canal at the 
base of the branchial crown. From the anterior limb of this outer circle a short 
wide trunk, the true branchio-cardiac or efferent vein of the branchise, opens forwards 
on the median line into the posterior border of the auricle of the heart. This efferent 
vein lies immediately over the hepatico-branchial or afferent vessel of the branchise. 
Thus it is that in the auricle of the heart, the blood from the liver-mass, having been 
aerated in the special respiratory organ, becomes mixed up with that from the other 
viscera, which has been returned through the general, though imperfect, respiratory 
surface of the skin, by the two great lateral systemic venous trunks before described. 
Having now gone over the general course of the circulation, there remains to be 
noticed the additional blood-propelling organ situated, as before mentioned, beneath 
the pericardium. Tins is the organ which Cuvier calls a vesicle acting as a reser- 
voir to a canal, which coming backward from the liver opens at the external orifice 
placed close to the anus. This canal and the vesicle act, according to the same high 
authority, as the agents for the production of an excrementitious fluid, which is pre- 
pared either by the liver itself in addition to the bile, or by some other gland, the 
lobes of which are so intimately interlaced with the lobes of the liver that the eye 
cannot distinguish one set from the other. M. Milne-Edwards conjectures, we see, 
in his ‘ Observations snr la Circulation,’ Article premier, in the Annales des Sciences 
Naturelles, 1845, ‘‘ that the pore which exists by the side of the anus in Doris may 
be for the purpose of admitting water into the interior of the organism, there to be 
directly mixed with the blood.” 
We began the study of this organ impressed with a high idea of the labour which 
Cuvier had bestowed upon it, and with every disposition to believe in the accuracy 
of his results ; but after repeated dissections, and injections, and careful observations, 
we find ourselves obliged, however reluctantly, to differ from the views that he and 
M. Milne-Edwards have taken of these parts, and we therefore submit the following 
description, which we confidently believe will be found correct by those who will 
take the pains to examine into the matter with the minuteness it demands. 
The vesicle, or heart 'f- as we term it, is a hollow pyriform organ, lying somewhat 
transversely under the I'ight side of the pericardium, with its base opening into that 
cavity just in advance of the posterior angle of the right side. The narrow end 
tapers to a tube, which after perforating the wall of the large sinus, to be presently 
mentioned, turns suddenly forwards along the median line of the liver, where it over- 
lies the great hepatico-branchial vein, partially concealing it. In this course the tube 
* Plate XVI. figs. 2 and 6. 
f Plate XI. figs. 1, 2, 3 and 4 ; Plate XII. figs. 1 and 5 ; Plate XVI. fig. 1. 
