606 DR. R. V. ERLANGER. 
transformed, and that a part of it corresponding to the duct 
forms a part of the genital apparatus. 
The next question is, what has become of the glandular 
part of the actual right kidney? R. Perrier (23), in his ex- 
tensive memoir on the anatomy of the kidneys of Prosobranchs, 
came to the conclusion that the only remaining kidney of 
most Prosobranchs is homologous with the actual right kidney 
of those forms which are provided with two renal organs. He 
inferred this from the fact that the actual right kidney of 
birenal forms is always the larger one, and always shows the 
characteristic brown renal secretory epithelium. I have 
already given my reasons against this inference, and will add 
that it seems more rational to admit that all the organs of the 
actual right side (left before the torsion) have disappeared in 
higher Prosobranchs. This opinion is supported by the facts 
that in Haliotis the right ctenidium is smaller than the left, and 
that in Turbo and Trochus the only remaining ctenidium 
and auricle are the actual left. KR. Perrier says that the actual 
left kidney, which is fast disappearing in Fissurella, much 
reduced in Patella, and highly modified in Haliotis, Tro- 
chide, and Turbo, where it is called papillary sac, has trans- 
formed itself into the so-called nephridial gland, a distinct 
part of the only remaining kidney of most Monotocards. 
According to Perrier the transition between Diotocards 
and Monotocards is formed by the Patellide or Hetero- 
cards. The left kidney has become located between the peri- 
cardium and the right kidney. The sinuses of both kidneys 
are in communication with those of the auricle. Supposing, 
says Perrier, that the thin wall between the left and the right 
kidney in Patella disappeared, the left kidney would become 
part of the right kidney ; thus apparently there would be only 
one kidney remaining, and the left one would exactly cor- 
respond to the nephridial gland. This hypothesis is realised 
by Ampullaria,! which, according to Bouvier (4), shows 
two kidneys, of which the actual right one (according to 
Bouvier) has the same shape and position as (ew. gr.) the only 
1 The species examined was leiotropic. 
