40 



(February 1889), aiid I do not doubt, that must of ihon will 

 survive the winter and next summer again produce a new series 

 of generations 1 . 



As seen from the above given dates, I Lave been enabled 

 to watch this form in the same aquary during no less than 4 

 successive years, each year exhibiting several successive ge- 

 nerations; but I have not yet met with a single male individual 

 though great quantities of specimens were at different times ex- 

 tracted from the aquary and submitted one by one to a close 

 examination. I thus believe to be fully justified in concluding, 

 that male specimens do not exist at all, and that this form of 

 course propagates in an exclusively parthenogenetical manner. 

 To the same conclusion I am led as regards the following spe- 

 cies, and also for a considerable number of the indigenous Cy- 

 prididae, of which never any male specimen has been met with, 

 this peculiar fact may be substantiated. 



In habits this species is a true bottom form, being, as 

 stated above, quite devoid of swimming power. Of course it 

 will generally be found at the bottom of the aquary, partly 

 creeping along the surface of the mud, partly burrowing 

 more or less deeply into the loose bottom deposit. Very often, 



slowly creeping up the walls of the aquary, or along the 

 steins of water-plants growing in the same; but when losing 

 its hold, it invariably sinks back to the bottom without 

 being able to support its body freely in the water. As 

 is also the case with several other Cypridida), the sheU, 

 when touching the surface of the water, continues to flotf 

 with the one valve quite out of the water, and it is tbeu 

 rather difficult to get it again submerged. In taking «P 

 T tlle '^ im 'y a small quantity of mud by the aid of a dip- 

 ping tube and placing it in a shallow vessel, as a watchglass, *j 

 specimens contained in the mud will soon come to sight » 



