98 M. L. Plate on Ectoparasitic Rotatoria 



fully developed, but the stomach only acquires its brown pig- 

 ment by the inception of food. The ova lying in one mass 

 are not all of the same sex, but among the preponderant 

 number of female ova we find here and there a male one. 

 As I often found only one female near such a breeding-spot, 

 and indeed upon the Nehalia infested, it follows that the same 

 animal may deposit ova of different sexes ; and this merits 

 notice because among the freshwater Rotatoria the indivi- 

 dual produces ova only of one sex, either male or female *. 



The male sexual organs of Paraseison are of very peculiar 

 structure, and differ considerably in the corresponding organs 

 not only from the species of Seison, but also from the other 

 Rotatoria. Like the female sexual organs they are paired 

 and placed dorsally with respect to the stomach. The testes 

 form two pyriforra organs (fig. 13, te), which traverse the 

 greater part of the length of the trunk, and turn their wider 

 end forward. Posteriorly they gradually narrow into an 

 efferent duct, which is curved towards the back. They do 

 not, however, always retain their position above the stomach, 

 but frequently slip down on the two sides of it. They open 

 into a rounded body {x), with regard to which, unfortunately, I 

 was unable to ascertain much. It appeared to me to be paired, 

 or at least divided by a groove into two lobes, and to stand in 

 connexion with a large pyriform organ {d. e/.), which at once 

 catches the eye. This sacciform structure becomes consider- 

 ably narrowed and then opens upon the dorsal surface at the 

 point where the neck and trunk pass into one another (a), and 

 in this terminal portion it shows a delicate ciliation, which, 

 however, lines the inner wall only for a short distance. The 

 broad posterior end of this peculiar organ, whicli seemed to 

 me to be formed of a structureless membrane, consists of a 

 homogeneous mass which is traversed by two contorted ducts 

 (v. d.) furnished with a ciliation striking backward ; the latter 

 open by two separate apertures into the cavity which lies 

 before them. As to their exact course and their connexion 

 with the body [x] which lies immediately behind them, I 

 could arrive at no definite opinion, as in the living animal 

 the investigation is rendered very difficult by its constant 

 movements, and dead specimens are always so contracted that 

 the parts in question are concealed. 



The male generative organs of Sei'son do not differ from those 

 of Paraseison just described so considerably as not to be com- 

 parable with them, and in accordance with this we have to 

 regard that structure (x) in our animal which receives the 

 efl'erent ducts of the testes as a seminal vesicle and the tor- 

 * See my previous memoir, I. c. p. 106. 



