ON THE PAIRED NEPHRIDIA OF PROSOBRANCHS. 9087 
On the Paired Nephridia of Prosobranchs, the 
Homologies of the only remaining Nephri- 
dium of most Prosobranchs, and the Re- 
lations of the Nephridia to the Gonad and 
Genital Duct. 
By 
Dr. R. v. Erlanger. 
With Plates XXXVI and XXXVII. 
IntRopUcTORY AND HiustroricaL Part. 
By the study of the development of Prosobranchs and 
fresh-water Pulmonates, especially of Paludina vivipara 
(8), Bythinia tentaculata (9), and Planorbis corneus 
(10), I was led to adopt Professor Ray Lankester’s (19) view 
on the homology of the only remaining kidney or nephridium 
of most Prosobranchs. I found that the kidney of Paludina 
and Bythinia, which in the adult lies to the left of the anus, 
was, before the torsion takes place, situated to the right of the 
anus, and consequently must be homologous to the actual left 
kidney of Fissurella, Patella, Haliotis, Trochus, &c. 
Whilst in so-called leiotropic species! the actual kidney is 
the left one, it isjust the contrary in dexiotropic species, such 
as Planorbis, where the actual right kidney is, before the 
torsion, situated to the left of the rectum. I also found in 
Paludina a rudiment of the actual right kidney lying before 
the torsion to the left of the rectum, and observed that its 
duct was converted into that of the genital gland. Comparing 
1 Leiotropie would correspond to the German term “rechtsge- 
wunden,” as used by conchologists ; dexiotropic to “linksgewunden,” 
