HERMAPHRODITISM IN MOLLUSCA. 21 



the mantle cavity, in front of the anus and more to the right ; 

 it is the female orifice (vii). 



The other branch immediately presents a glandular mam- 

 millated mass with closely packed lobules, and then extends 

 forward under the integument over the neck of the animal as 

 far as a considerable projection of the body-wall on the right 

 side, the penis, which it traverses from end to end (fig. 1, v). 



The structure of the reproductive apparatus thus differs 

 from that of Valvata in the presence of glands upon the her- 

 maphrodite portion of the duct, and by the absence of a dif- 

 ferentiated '^ uterus " in the female portion. 



The glands of the hermaphrodite duct (fig. 1, x) do not 

 appear to me to be vitellogenous or albuminiparous glands 

 (judging, at least, from the imperfectly preserved specimen 

 which I have examined). I regard them rather as vesiculse 

 seminales. 



As for the two appendages of the female duct, the elongated 

 pouch is a receptaculum seminis (or poche copulatrice), 

 and the flattened pouch (fig. 1, in) is the mucous or jelly 

 gland. Lastly, the glandular mass of the male duct can be 

 termed the prostate, as in other hermaphrodite Gastropods. 



If the presence of two genital apertures could not, in itself, 

 demonstrate the hemaphroditism of Onchidiopsis, the struc- 

 ture of the genital gland is sufficient to remove all doubts. 

 This gland is formed of parallel caeca, bifid at their extremities 

 (fig. 3) : these terminal divisions are ovogenous, while the 

 proximal portions of the duct are spermatogenous. As a result 

 of this arrangement the gland appears to be composed of a 

 superficial or external female portion, and of a deeper or 

 central male portion. However, these two regions are not 

 demarcated with any regularity, and in the middle portion 

 male and female acini can be seen in sections lying side by 

 side (fig. 3). At all events, the products of the two sexes 

 either do not arise in the same caecum or they do not arise in 

 the same region of a C£ecum. 



According to Bergh's observations, Marsenina appears to 



