ON THE PAIRED NEPHRIDIA OF PROSOBRANCHS. 603 
As regards the presence or absence of reno-pericardiac ducts 
in Patella I have come to the same conclusions as for 
Fissurella, Emarginula, and Puncturella, and must 
also add Tectura to the list of Prosobranchs having no 
communication between the kidneys and the pericardium. 
Injections made according to my method, which I owe to Pro- 
fessor Mayer’s kindness, led me to the same conclusions. When 
a higher pressure is used the injection may penetrate into either 
kidney, but generally it is easier to drive it into the left. The 
places in which this happens are always the same, and can 
be readily found by dissections and sections without using 
injections. 
Fig. 25a shows that towards the latter end of the mantle 
cavity (M.) the left kidney comes very near the wall of the 
pericardium. In this section there is still a thickish muscular 
partition between the left kidney (V/.) and the cavity of the 
pericardium. This is the continuation of the partition between 
the mautle cavity and the pericardium. Still further back 
(fig. 255) the mantle cavity (/.) recedes more and more from 
the pericardium (Pe.), and the muscular partition entirely 
disappears in a spot (+) which very probably corresponds to 
an abortive funnel. In this place the cavity of the left kidney 
is only separated from that of the pericardium (Pc.) by the 
secreting epithelium of the kidney, the tunica propria of the 
same organ, and the flat epithelium of the pericardium. This 
accordingly is the likeliest spot for an injection to break 
through either from the pericardium into the left kidney or 
vice versa. Even when using an immersion I was unable to 
find the smallest opening in this place when examining series 
of a specimen which had not been injected. I wish to remark 
here that Mr. Cunningham states that he has been able to 
trace the reno-pericardiac ducts in sections through an 
uninjected specimen. 
I myself have already pointed out that to my mind the 
method of injection is of very small value in such cases, and 
very likely to mislead the investigator. I remind the reader 
that many French anatomists, who seem to be particularly 
