616 DR. R. V. ERLANGER. 
condition was an unpaired gonad. This having become 
separated off from the pericardium was accordingly obliged to 
form a new communication with the outer world. In Zygo- 
branchs, Tectibranchs, and in Scaphopods the gonad 
enters into communication with the actual right nephridium 
by bursting open its wall, or by opening into it by a special 
duct, probably evolved from a part of the gonad itself. In 
higher Prosobranchs the genital duct is probably the duct of 
the actual right aborted kidney (Paludina). In the archaic 
forms of Lamellibranchiata, which according to Pelsener (22) 
are modified Prosobranchs, such as Nucula, the genital 
products are expelled into the initial part of the nephridia, 
that is to say, alongside of the reno-pericardiac funnel, 
while as we proceed higher, independent genital ducts 
are formed. In Chitons we find. an independent pair of 
genital ducts, as in Cephalopods. It is as yet not known 
whether these ducts are in any way related to those of the 
nephridia. 
According to Grobben (12), Sepia, probably the most 
archaic form, shows a large celom, communicating with the 
nephridia by two openings or funnels. The cavity of the 
celom is coated with an epithelium, and encloses in its 
anterior portion the heart with its vessels, the branchial 
hearts and the pericardial gland, formed by differentiated 
peritoneal epithelium. The hinder portion of the cclom, 
divided off incompletely from the anterior one by a septum, 
encloses the gonad, which probably belonged originally to the 
epithelium of the peritoneum, and the stomach. 
All the evidence which I have collected in the comparative 
part of this paper tends to show that the molluscs are true 
ccelomate animals, and that the condition of the genital and 
renal organs is closely similar to that of primitive Annelids. 
Before concluding this paper I wish to remark that I am 
fully prepared to have the truth of my statements on Fissurella 
and Patella questioned. I have given myself the greatest 
trouble to find both reno-pericardiac ducts. Being unable to 
see the left one, the existence of which I was most anxious to 
