604. DR. R. V. ERLANGER. 
partial to injections, have, in molluscs, described a very com- 
plicated system of arteries, capillaries, and veins which were 
simply the artificial results of the injections. 
A corresponding spot also exists in the right kidney, at the 
end of the so-called subanal tract of the right kidney (fig. 20). 
In this place, in which both Lankester and Cunningham have 
stated they found the reno-pericardiac duct, the right kidney 
also comes right up to the pericardium. It remains, however, 
separated from its cavity by a thin layer of muscular tissue. 
This circumstance explains why it is easier to get the injection 
from the pericardium into the left kidney than into the right 
renal pouch, and also accounts for the fact that Ray Lankester 
(18) first found the left kidney of Patella opening into the 
pericardium. 
Tectura, as has already been mentioned, closely resembles 
Patella. There, nevertheless, are a few points on which I 
desire to direct the reader’s attention. As in Puncturella 
compared to Fissurella and Emarginula, the visceral 
hump is far better developed in Tectura (fig. 17, H.) than in 
Patella. Both in Tectura and Puncturella the difference 
in the size of both kidneys is smaller; both renal pouches are 
simple in their shape, that is to say, less ramified. 
Fig. 24, a frontal section through the pericardium (Pe.) and 
both kidneys of Tectura, is given to show that the left kiduey 
(WN/.), which is still smaller than the right (JVr.), lies entirely to 
the front of the rectum (#.), and in the same longitudinal 
line as the right kidney. ‘This fact will be made use of in the 
comparative part of this paper. 
CoNCLUSIONS AND COMPARATIVE Part. 
The results of this investigation may be summed up as 
follows : . 
Trochus, Turbo, and Haliotis possess a left reno-peri- 
cardiac duct only. 
Fissurella, Emarginula, Puncturella, Patella, and 
Tectura possess no reno-pericardiac duct whatever, 
