RENAL ORGAN IN THE NUDIBRANCHIATE MOLLUSCA. 525 
not to be surprised at finding that the homologous chambers in the Nudibranch and 
Cephalopod contain dissimilar organs. "This, however, is applicable more particularly 
to the pericardial chamber of the former, in which the heart is lodged. But we have 
seen that this chamber is developed upwards and backwards in the Cephalopod, and is 
consequently drawn away from the heart, which occupies a position between the two 
chambers. Now, were the ovary and stomach pushed in the same direction, it is easy to 
understand how they might become enveloped in the membranous wall of the chamber, 
and ultimately enclosed within its cavity. 
The renal chamber proper in the Nudibranchs lies in contact with the intestine and 
the hepatico-branchial vein, which latter is the representative in these animals of the 
vens cavee of the Cephalopods. The lower portion of the intestine indeed is partially 
enveloped by the walls of the chamber. There is therefore no difficulty here; for by a 
slight modification in development both these organs might be thrust into the chamber, 
and, from the change of the relative position of the stomach and liver that has taken 
place in the Cephalopod, it is obvious that the hepatie ducts might likewise be enveloped 
by it; and so with the several other organs. 
If, then, this reasoning be correct (and it seems scarcely possible to doubt it), the renal 
chamber in the Nudibranch is the homological representative of the, pseudo-pericardium 
or renal chamber proper of the Cephalopod, or rather perhaps of the right half of it, the 
left half, together with its external outlet and passage of communication, having been 
atrophied in the Nudibranch. In both animals this chamber opens externally, and in 
both it communicates with another chamber,—in the Nudibranch with the so-called 
pericardium, and in the Cephalopod with the genital chamber—which two latter chambers 
are also homologous. The pyriform vesicle is apparently a mere enlargement of the 
tubular passage of communication between the two chambers. In the Octopodide there 
is a not very dissimilar enlargement of this tube, but apparently for a different functional 
purpose. | 
It thus appears that in both the Nudibranchs and the Cephalopods the renal organ is 
extensively diffused throughout the organism, and that it is universally divided into two 
portions or chambers, one of which, the renal chamber proper, is more or less glandular, 
and has the office, through the agency of secerning cells, to eliminate from the blood the 
deleterious urinary matters. This is apparently its special function, though it would 
seem in many instances also to have, in common with the other portion or chamber (the 
so-called pericardium in the Nudibranch, and the genital chamber in the Cephalopod), to 
act as a receptacle for the superabundant fluids, perhaps little more than water, that may 
be supposed to exude from the tissues of the various contained organs. 
This duality of the kidney we have seen also to exist in the Brachiopod, the Lamelli- 
branch, and in Plewrobranchus. It is for future research to show how far this condition 
of the renal organ extends throughout the Mollusca. 
The renal organ in the Cephalopod differs from that of the Nudibranch chiefly by 
being more extensively developed. This is more particularly the case with respect to 
the genital chamber, which frequently contains many organs. The homologous chamber 
in the Nudibranch contains always, and never anything more than, the heart. In both 
VOL. XXIV. oY 
