220 GASTROPODA. 



which, in the male apparatus, runs from the testis to the commence- 

 ment of the so-called primary (ectodermal) efferent duct. The whole 

 of the remaining efferent apparatus in the female corresponds to the 

 primary efferent duct in the male, and the former, like the latter, 

 opens into the mantle-cavity. There is, in the female, no part corre- 

 sponding to the secondary efferent apparatus of the male. Apart from 

 this last portion the genital apparatus in the male and in the female 

 thus agree closely in their development, the principal constituent 

 parts being apparently quite homologous (v. Erlanger). 



The relation of the germ-glands to the pericardium, which was only con- 

 jectured to exist in the Lamellibrauchia (p. 82), is definitely proved by V. 

 Erlanger to exist in the Gastropoda. The genital glands arise as growths 

 of the pericardial wall, and thus bear to this latter the same relation as do the 

 genital products in the Annelida to the peritoneal epithelium (Vol. i., p. 297). 

 In this way we obtain a further support for the coelomic nature of the peri- 

 cardial sac. Since, in the lower forms, the nephridia function in conducting 

 the genital products to the exterior, it appears as if, in the Gastropoda, the 

 nephridium, which no longer functions as a kidney, might become directly 

 modified as the efferent genital duct. As we have seen in the Solenogastres 

 (p. 9), the nephridia transmit the genital products, and even in some Proso- 

 branchs (i.e., the majority of the Diotocardia) the right nephridium serves 

 in addition as a genital duct ; such a modification of the efferent renal ducts 

 is therefore not surprising. 



• 



The hermaphrodite genital organs of the Pulmonates have repeatedly 

 been made the subject of careful ontogenetic research (Eisig, No. 26 ; 

 PiOuzaud, No. i'4 ; Brock, No. 16; Simroth, No. 119; Klotz, No. 

 54), but so far no satisfactory conclusion as to their origin has been 

 arrived at. The conditions are here very complicated and obscure. 

 The point of greatest importance is to ascertain the relations between 

 the various ducts of the hermaphrodite forms and the simple efferent 

 apparatus of the dioecious forms and finally to trace the former to the 

 latter. We cannot state definitely that the separation of the sexes is 

 the primitive condition, although this seems highly probable, since the 

 older (Gastropods (the Diotocardia) are dioecious and the most special- 

 ised forms (Opisthobranchia, Pulmonata) are hermaphrodite. As the 

 accounts so far published do not enable us to obtain a clear concep- 

 tion of the development of the hermaphrodite genital organs, it is 

 only possible to consider them by the light of the better understood 

 development of the dioecious Prosobranchia. 



At the very outset of this investigation, however, a difficulty is 

 occasioned by the question as to whether the genital apparatus is 

 derived from one common rudiment or from two or three distinct. 



