28 PAUL PELSENEEK. 



(6) Anatinacea and Poromyidse. 



Several years ago (28) I made known the hermaphroditism 

 of Thracia^ Lyonsia, Lyonsiella (Anatinacea), and of the 

 allied family Poromyidse (Septibranchia) ; and at the same 

 time I confirmed its existence in Pandora, in which it had 

 already been once affirmed (29). Having thus demonstrated 

 the monoecious nature of all the genera of Anatinacea which I 

 had examined, I was led to believe in the hermaphroditism of 

 the entire group, a conclusion which accorded well with 

 Lacaze's observations upon Aspergillum (30). 



Since that time I have been enabled to study one other 

 genus of this group, Clavagella, although, in spite of nume- 

 rous eflforts, I have not succeeded in obtaining either Anatina 

 or Pholadomya, which appear to be rare. I have observed 

 the same monoecious arrangement in Clavagella as in the 

 other Anatinacea previously studied. There can accordingly 

 be no doubt as to the hermaphroditism of this group, since no 

 genus belonging to it has yet been found to be dioecious. 



Like all the Anatinacea, Clavagella possesses two testes, 

 two ovaries, and four distinct genital apertures. The two 

 testes are symmetrically placed in the pedal projection (fig. 15, 

 viii), i.e. in the ventral part of the body; the two ovaries, 

 which are much more voluminous, compose almost the entire 

 posterior visceral mass as far as the nephridia (figs. 15 and 16). 



The genital pores are situated behind ; those of the testes 

 on the sides of the base of the foot, ventrally or internally to 

 the visceral commissure (fig. 14, vii); those of the ovaries a 

 little further back, dorsally or externally to the same commis- 

 sure (fig. 14, iv) . 



ii. pflylogenetic evolution of the hermaphrodite 

 Gland in Mollusca. 



If any other group of hermaphrodite animals is taken into 

 consideration, one is struck by the general uniformity in the 

 structure of the genital glands. In the Mollusca, on the other 



