520 MR. A. HANCOCK ON THE STRUCTURE AND HOMOLOGIES OF THE 
The nature of this complicated organ in the Nudibranchs can scarcely be doubted. Tt 
is clearly an apparatus for eliminating something from the blood that has to be expelled 
out of the system; and from analogy this matter may fairly be assumed to be urinary. 
The renal chamber proper is a glandular organ, as demonstrated in the Dorides; and in 
Bornella and Scyllea it has assumed the form of a true gland. It is therefore probable 
that by this portion of the apparatus, and also by the glandular portion of the pyriform 
vesicle, the more strictly urinary matters are abstracted, the pericardial chamber fur- 
nishing serum or perhaps little more than pure water, which may be supposed to exude 
from the heart, particularly from the auricle, the walls of which are exceedingly delicate. 
The pericardial fluid will be drawn into the pyriform vesicle by the agency of the 
vibratile cilia clothing the plice ; the sphincter muscles will then come into play, closing 
the communicating orifice, and the contained fluid will be forced by the pulsatile action 
of the organ (the walls of which we have seen to be muscular) into the trunk tube or 
central portion of the renal chamber, where it will mingle with the more solid urinary 
products of that organ, and be expelled along with them through the minute pore 
associated with the anal nipple. That this is the probable action of these parts is 
evinced by what may be observed in living Nudibranchs. I have frequently seen, in 
small, transparent individuals, vibratile cilia in motion, at the orifice of a vesicle having 
the appearance of this pyriform organ ; and the vesicle itself may occasionally be observed 
to contract. But, however this may be, it is evident enough that the pyriform vesicle is 
for the passage of fluid from the one chamber to the other. 
It is worthy of remark that in the higher Nudibranchs, as in Doris for instance, the 
essentially urinary matters are abstracted from the blood that circulates in the liver- 
mass, which is composed of the liver and ovary, there being a special arrangement of the 
vascular system in connexion with the renal chamber for the purpose; and this is the 
only blood of the entire animal that passes through the special aérating organ. In the 
lower forms these matters are eliminated from the blood that circulates in the visceral 
chamber, consequently from the general supply previous to its return to the vascular 
centre. Hence it may be inferred that in the former case the organ is more highly 
specialized than in the latter, in which it is extremely diffused. In Seyllea the kidney 
holds a middle position in this respect; for though the ramifications of the organ are 
extensively distributed, a considerable number of the branches are nevertheless inti- 
mately connected with the liver and ovary, particularly with the latter; they therefore 
probably have some relation to the blood-system in these organs. Many of the branches, 
however, lie free in the interstices between the viscera. 
Such being the function of this enigmatical apparatus, it can scarcely be supposed to 
perform the work of a water-system as generally understood. M. Milne-Edwards suggests, 
in his * Observations sur 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.” In our examination of the organs in connexion with this pore, 
we have seen nothing to warrant this belief; on the contrary, the anatomy of the 
various parts militates against it. We have seen that the renal organ forms à closed 
