HERMAPHRODITISM IN MOLLUSOA. 19 



Hermapliroditism in MoUusca. 

 By 



Dr. Paul Pelseiieer (Ghent). 



With Plates 4—6. 



Contents. 



I. Hermaphroditism in Mollusca. 



1. Ampbiueura. 2. Gastropoda. 3. Lamellibrancbia. 



II. Phylogenetic Evolution of the Hermaphrodite Gland in 



Mollusca. 



1. Gland with hermaphrodite acini. 



2. Gland with separate male and female acini. 



3. Gland with separate male and female regions. 



4. Separate male and female glands in the same individual. 



III. Physiological Evolution of Hermaphroditism in the Molluscan 



Individual. 



IV. Origin of Hermaphroditism in Mollusca. 



1. Hermaphroditism has arisen from the unisexual state. 



2. Hermaphroditism has been grafted on the female organism. 

 V. Conclusions. 



I. Hermaphroditism in Mollusca. 



Hermaphroditism is found to occur in every class of Mol- 

 lusca except the Cephalopoda and Scaphopoda. 



1. Among Amphineura, in all the Neomeniidse. 



2. Among Gastropoda^ in four genera of Streptoneura 

 (Valvata, Onchidiopsis, Marsenina, and Eutoconcha), 

 and in all the Euthyneura (Opisthobrauchia and Pulmonata). 



3. Among Lamellibrancbia, in various species of Pecten, 



