Development of Rotifer vulgaris. 127 



that Enteroplea hydatina was the male of Hydatina senta and 

 Notommata granulans that of N. brachionus. 



Three years later (1858) F. Cohn communicated the 

 results of his further investigations in an interesting memoir 

 which appeared under the title of ■' Remarks on the Rota- 

 toria," in the ninth volume of this ' Zeitschrift.' In the 

 concluding pages of this publication Cohn expresses the 

 opinion that in the Rotatoria a peculiar form of alternation 

 of generations occurs, thus constituted : — " the fecundated 

 females alone deposit hard-shelled ova, which pass through 

 the winter, while the unfertilized summer eggs are developed, 

 from which proceed directly either females again or, at certain 

 seasons, males also." 



Valuable information as to the anomalous structure of many 

 Rotatoria was given in a memoir by Metschnikoff which was 

 published in 1866 *. It treats of Apsilus lentiformis } the 

 most remarkable peculiarity of which consists in the absence 

 of any vibratile apparatus. This Rotifer also has separate 

 sexes. This fact was first ascertained by Prof. R. Leuckart. 

 Here also it was proved that the male is destitute of all 

 traces of the digestive organs, while, on the other hand, the 

 aquiferous system shows a considerable development. 



It was ascertained by W. Salensky, who observed the 

 embryonic evolution in Brachionus urceolaris (1871), that in 

 this Rotifer the development of the two sexes takes place 

 quite concordantly in the first stages. Only at a later period 

 does the intestinal canal, which originally occurs as an in- 

 vagination on the ventral surface in both males and females, 

 undergo in the former a retrogressive metamorphosis and 

 become aborted f. 



Quite recently (1883) a memoir by Karl Eckstein % upon 

 the Rotatoria of the neighbourhood of Giessen has been pub- 

 lished, containing numerous valuable observations. With 

 regard to Rotifer vulgaris, however, even this memoir gives 

 us very little information, and in the following statements I 

 find myself thrown principally upon my own observations. 



II. The Material 



for my observations I obtained in two ponds situated directly 

 in front of my house at Curmersdorf. Subsequently I ob- 

 tained it from the " Froschgraben " which stretches between 

 the town of Hirschberg and the village of Grunau, a locality 

 which, after Von Flotow's and F. Cohn's investigations upon 



* Zeitschr. f. wiss. Zool. xvi. (1860), pp. 346-356. 

 t Ibid, xxii. (1872), pp. 455-466. 

 X Ibid, xxxix. (1880), pp. 343-443. 



10* 



