106 ISABELLA M. DKUMMOND. 



the Haliotidrc and Trochidas a very small definitive left 

 kidney is present, and that the large kidney is the definitive 

 right, and still maintains its connection with the genital 

 organ. 



It might seem that von Erlanger (5 and 6, see also 7) had 

 already sufficiently demonstrated from embryology that the 

 homologies which Pelseneer believes to hold for Haliotis 

 and Trochus are equally true for Paludina. To this, however, 

 Haller (11) objects that in a highly organised form, such as 

 Paludina, torsion is very likely abbreviated, and the organs may 

 be formed in their definitive position. This view is, it seems 

 to me, quite untenable from von Erlanger's description, while 

 a further study of the development of this form shows even 

 more clearly that a complete rotation of the organs through 

 180° actually takes place in the course of development,^ and 

 that the adult kidney arises on the right, and ends on the 

 definitive left side of the body. I have, fortunately, been 

 able to add further to this evidence by showing how the 

 gonad still stands in close relation with the definitive right 

 kidney, though this has altogether lost its excretory character, 

 and that no such separate duct as Haller describes is ever 

 formed. It seems, then, that there is every reason for 

 believing that the definitive right kidney has persisted 

 throughout the Prosobranchia as the genital duct, in some 

 cases, as in Haliotis, performing also its renal functions, 

 while in Paludina these latter are carried on altogether by 

 the left kidney, the right functioning only as a gonaduct. 



With regard to the manner of communication between the 

 two organs, Pelseneer and Haller are also in disagreement. 

 In the Docoglossa, at least, Haller describes a ventral 

 coclomic chamber through which the genital products must 

 pass in order to reach the kidney ; while Pelseneer regards 

 this so-called coelom as merely a portion of the kidney itself, 

 the gonad being in direct communication with this latter, and 

 altogether separated from the coelom, which is only repre- 

 sented by the pericardium. Whether Haller believes in a 

 ' Tor evidence upon this point, sec Part II of tliis jjaper. 



