ON THE PAIRED NEPHRIDIA OF PROSOBRANCHS. 591 
and consequently in a centrifugal direction. By request of 
Professor Ray Lankester, I made some more injections from 
the kidneys, with the same results, which I have already 
described. Personally I do not think the latter method of 
injection a good one. I consider it even less reliable than 
the first, as a great many animals possess a valve between the 
pericardium and the reno-pericardiac duct, in order to prevent 
the excreted liquid from flowing back into the pericardium. 
The shells of most of the species of Prosobranchs studied 
by me in the course of these investigations were determined 
by Professor Boettger, in Frankfort-on-the-Main, and Dr. 
Kobelt, in Schwanheim, near Frankfort-on-the-Main. I beg 
both these gentlemen to accept my thanks for having so 
readily fulfilled my request. 
Descriptive Part. 
I propose to begin with Haliotis and Trochus, where a 
reno-pericardiac canal (left) really exists. I shall afterwards 
describe the other forms in which no such a structure exists. 
I adopt this order so as to show that I have not overlooked 
the communication between pericardium and kidney, which is 
really quite easily to be found in Haliotis, Trochus, and Turbo, 
even by dissection alone, whilst in Fissurella and Patella no 
trace of such a structure could be found. 
1. Haliotis tuberculosa. 
This species has been studied by v. Jhering (16), Weg- 
mann (27), Haller (13), and Perrier (23). I am happy to be 
able to confirm Jhering’s, Wegmann’s, and Perrier’s state- 
ments. Jhering’s figures are certainly a little schematic, as 
Haller remarks ; but whilst Haller’s figures are very good and 
exact, his interpretation is quite incorrect. He considers the 
duct of the right kidney exclusively as the genital duct, and 
describes a communication between the right kidney and the 
left (Haller’s papillary sack) which really does not exist at all. 
Fig. 1, a view of the dorsal surface of Hal. after removal of 
the shell shows the pericardium (Pc.) in situ at the hinder 
