20 PAUL PELSENEER. 



Ostrea, and Cardium; in Entovalva, the Cycladidse, the 

 Poromyidse, and all the Anatinacea. 



1. Amphineura. 



(1) Neomeniidae. — In each of the two contiguous herma- 

 phrodite glands of these animals the ova arise in the axial half 

 of the organ, and the spermatozoa in the lateral half (1). 



(2) Cryptochiton . — According to Middendorf (2) this genus 

 is hermaphrodite. I have, however, been able to obtain a 

 specimen in alcohol of this form (C. Stelleri, from the North 

 Pacific), and have found it to present a distinctly unisexual 

 condition, as in Chiton. I have also satisfied myself that 

 the sexes are separate in Chitonellus larvseformis ( = 

 fasciatus) and Cryptoconchus porosus (or monticu- 

 laris). Thus the dioecious condition is universal in the Poly- 

 placophora. 



2. Gastropoda. 



(1) Valvata. — The hermaphrodite gland of this genus is 

 formed of acini, all producing ova and spermatozoa (3). 



(2) Marsenina and Onchidiopsis (of the family Larael- 

 lariidae). — While the hermaphroditism of Valvata has been 

 recognised by a fair number of zoologists, that of the two 

 genera just named has only been aflSrmed by Bergh (4). 



As the number of monoecious Streptoneura is extremely 

 limited, an examination of these two genera was desirable in 

 order that Bergh's discovery might be confirmed and his state- 

 ment of facts extended. I have only succeeded in obtaining a 

 single specimen of Onchidiopsis greenlandica, and upon 

 it I have made the following observations. 



The genital gland occupies the posterior part of the visceral 

 mass. Its duct is provided with an accessory mass formed of 

 closely packed, narrow, tubular cseca ; it then bifurcates, and 

 the more lateral branch (the right), after first receiving a large 

 bent pouch (fig. 1, iv), immediately thickens before opening to 

 the exterior, and again receives on its right side a large pouch 

 of flattened form. The aperture of this branch is situated in 



