RENAL ORGAN IN THE NUDIBRANCHIATE MOLLUSCA. 517 
continued, much reduced in size, for some distance down the ezcal tube. The peri- 
cardial chamber presents nothing peculiar, except that it is unusually large. 
In the form now béfore us the renal organ is comparatively simple in its structure ; 
but in those that are to follow, much complication will be observed; nevertheless, in 
them, as well as in the former, it is distinctly divisible into the two principal component 
parts, which we have seen to exist in all the species examined. An interesting example 
of this complicated condition of the organ is found in Bornella digitata, a very curious 
animal from the Indian seas, closely related to Dendronotus. | 
The pericardial chamber (Pl. LVII. figs. 1 & 6) in this species presents nothing re- 
markable; neither does the pyriform vesicle, though it opens into the former further 
backward than usual, and close to the right side, under the auricle. It is the part desig- 
nated as the renal chamber proper that exhibits the interesting and extensive modifica- 
tions alluded to. This portion of the renal organ (figs. 1 & 2 j) assumes the form of a 
long, wide tube, with delicate, almost transparent walls, extending along the dorsal 
surface of the viscera nearly from one extremity of the body to the other. In front this 
tube lies beneath the perieardial chamber, and at this point it bifureates, the two 
branches being almost as wide as the trunk. The left branch lies above the stomach, 
the right above the reproductive organs. The pyriform vesicle penetrates the trunk, and 
opens into it close to the point where the bifurcation takes place; and immediately 
behind this a'slender tube is given off from the right side, which passes along the dorsal 
Surface of the rectum, and terminates at a minute orifice immediately above the anal 
nipple. : 
The whole of this tubular chamber, including the anterior bifurcation, gives off from 
both sides numerous slender offsets, which for the most part bend downwards and, 
embracing the viscera, ramify over them. These ramifications terminate in blind sacs, 
and have their extremities occasionally rounded and enlarged. The branches are not 
adherent to the organs upon which they rest, but lie free amidst the loose cellular tissue 
that binds the viscera to the skin; and many of the terminal extremities penetrate the 
intermuscular spaces of the foot, others follow the gastro-hepatic branches into the base 
of the branchial papilla. The posterior trunk terminates, close to the extremity of the 
visceral mass, in a ramified branch similar to the lateral branches, and the members of 
the anterior bifurcation end in the same manner not far behind the buccal organ. 
This“much-ramified organ is lined throughout with a coating of opake, pale, granular 
matter, composed of minute cells. In the trunk this coating is very thin, but is much 
thicker in the branches (Pl. LVII. figs. 4 & 5), where it is thrown into longitudinal 
folds ; consequently the latter, on account of their opacity, are more conspicuous than 
the former, though this is very much larger. 
Now it is quite evident that we see, as it were, in this beautifully developed organ an 
unravelled gland, which, from its peculiar structure, throws much light on the nature of 
this organ in the species previously described. In Bornella it is no longer combined 
with the liver-mass (which in this form is broken up), though partially retained in the 
visceral chamber. Owing to this fact the gland is distinctly visible in all its parts, and 
it is perfectly clear that it is in no way anatomically or functionally connected with the 
VOL. XXIV. 3x 
