288 Dr. F. Leydig on Ilydatina senta. 



XXIX. — On Hydatina senta. By Dr. F. Leydig*. 

 [With a Plate.] 



Whoever has taken notice of the literature of the Rotifera is 

 aware that for a long time the sexual relations of this group of 

 animals were involved in obscurity ; for although recent observers 

 were agreed that the parts described by Ehrenberg as testes, 

 seminal ducts, and seminal vesicles, can by no means have any 

 such import, still, on the other hand, no undoubted male sexual 

 organs and seminal corpuscles could be detected. 



The discovery of the sexual relations was made by Dalrymplef. 

 He proved that Notommata anglica is not hermaphrodite, but 

 that it possesses separate sexes. Subsequently the present 

 writer made known the male of a new species J, nearly allied 

 to the English one ; and on comparing the structure of the 

 Rotatoria, with which I had become acquainted by my own ob- 

 servations, with the published statements, I was compelled to 

 conclude, " that male individuals of other species have also been 

 already described, but that they have been described under the 

 title of peculiar genera and species." And amongst other things, 

 I asserted that to my mind it was " beyond all doubt " that the 

 Enteroplea Hydatina is the male of Hydatina senta. 



Unfortunately, I could not at that time meet with this Rotifer 

 in the neighbourhood of Wiirzburg, although, as many observers 

 state, it is one of the very common and widely distributed spe- 

 cies ; and this was the more to be regretted, as, in consequence 

 of Ehrenberg's descriptions, the Hydatina senta as it were played 

 the part of a typical representative of the Rotatoria in books. 

 Nevertheless I had the satisfaction of seeing my assertion with 

 regard to the male nature of Enteroplea Hydatina confirmed by 

 another observer. Cohn namely § had the opportunity of exa- 

 mining this animal, and found the testes and motile spermatozoa. 

 During the present spring, in the early part of March, I fished 

 a small pool near Wiirzburg, which is dry in summer, and there 

 obtained Hydatina senta in innumerable multitudes; at that 

 time the animal was almost the sole inhabitant of the water, for 

 besides it I only observed a few Vorticellce, with here and there 

 a Brachionus and some larvse of Diptera. Towards the end of 

 March they had increased to so extraordinary an extent, that 



* Translated from Miiller's Archiv, No. 4, June 185/, p. 404. By 

 W. S. Dallas, F.L.S. &c. 



t Phil. Trans. 1849. 



X Ueber den Ban und den syst. Stellung der Raderthiere ; Zeitschr. fiir 

 wiss. Zoologie, 1854. 



§ Zeitschr. fiir wiss. Zoologie, 1855. 



