RENAL ORGAN IN THE NUDIBRANCHIATE MOLLUSCA. 523 
arranged after the same manner as that in the Nudibranchs. In Pleurobranchus there 
is the same closed pericardial chamber (Pl. LIV. fig. 4), communicating through its floor 
with a long glandular tube, the anterior extremity of which is swollen a little and cor- 
responds to the pyriform vesicle. The tube tapers to the other extremity, which, passing 
backwards, opens into a large renal chamber that communicates with the exterior through 
a small pore situated immediately below the gill. This tubular connexion between the 
pericardium and the renal chamber seems to have escaped the notice of M. Lacaze- 
Duthiers. 
The coexistence of this opening in the branchial vein along with a renal organ so con- 
structed makes it more unlikely that water should be received into the interior through 
the agency of the latter organ, in either the Lamellibranchs or Nudibranehs. We 
should rather look for some special means for the admittance of fluid from the exterior, 
if, indeed, water be absorbed directly by the vascular system in either of these two 
Molluscan groups. | 
In the Nudibranchs we have seen that the renal organ is divided into two principal 
chambers, the perieardial and the renal chamber proper, and that these communicate 
with each other through the agency of the pyriform vesicle. The renal organ in the 
Lamellibranchs is likewise divisible in the same way into two portions. And it is inter- 
esting to remark that the Brachiopods also have the renal organ composed of two well- 
marked divisions—namely, the great perivisceral chamber with its extensive ramifications, 
and the renal organ proper or the oviducal passages. 
This twofold character is also distinctly observed in the Cephalopoda. In this class 
of highly organized Mollusks the two renal chambers are extensively developed; and 
on comparing them with the corresponding parts in the Nudibranchs, many curious 
and instructive modifications will be observed. The renal chamber proper (Pl. LIX. 
fig. 2) is plaeed towards the underside of the body, and opens externally into the 
branchial chamber by two nipple-formed orifices. This is the pseudopericardium of 
authors. It, however, never contains the heart, but, along with other organs, always the 
ven: cavee with their glandular or renal appendages. In the Octopodide it contains 
_ usually only these latter organs, and is divided longitudinally by a membranous septum 
into two lateral halves. 
This chamber communicates with another, the genital, by two lateral passages. The 
genital chamber occupies the posterior extremity of the body, and is extensively deve- 
. loped in the Loliginide, in which it always contains the male or female secerning organ, 
the stomach, cecum, and the branchial hearts. In the Octopodide it contains the above- 
named reproductive organs only. This chamber is the equivalent of the pericardial 
chamber in the Nudibranchs. 
Now, the first thing that strikes us on comparing these with the corresponding parts 
in the Nudibranchs is the bilateral symmetry which they exhibit in the Cephalopoda. 
In the Nudibranchs we have seen that there is but one external orifice, and that it is 
placed towards the right side of the anus, the left being atrophied. In the Cephalopod, 
on the contrary, there are two such orifices, and they are situated symmetrically towards 
the sides, with the intestine between them. In the Nudibranchs, again, there is but one 
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