Reproduction and Development of Rotifer vulgaris. 125 



XIII. — On the Reproduction and Development o/'Rotifer 

 vulgaris. By Dr. Otto Zacharias *. 



[Plate V. B.] 



Rotifer vulgaris, as its name implies, is one of the com- 

 monest of the Rotatoria. Spallanzani observed it and made 

 interesting experiments upon its faculty of reviving after 

 complete desiccation. It is to be met with abundantly 

 throughout the whole year in ponds, ditches, and pools. But 

 notwithstanding the constant opportunity presented for its 

 examination, Rotifer vulgaris has not yet been accurately 

 investigated with regard to either its anatomical structure or 

 its developmental history. 



In the following pages I give a detailed report of the 

 results of an investigation of this Rotifer commenced in 

 February and continued until the middle of July in the 

 present year (1884). 



I. Historical. 



Thirty years ago it was regarded as unsettled whether the 

 Rotatoria are of separate sexes or hermaphrodites. The 

 standpoint of investigation at that time will be best charac- 

 terized by a passage from Siebold's ' Comparative Anatomy,' 

 which I will here cite verbatim. It runs as follows : — "As 

 the Rotatoria are provided with such distinct female sexual 

 organs, one might also justly infer the existence of male 

 generative organs in these animals ; but notwithstanding the 

 most careful endeavours, no satisfactory result as to the true 

 nature of their male sexual apparatus has hitherto been at- 

 tained, so that it is still doubtful whether the Rotatoria are 

 hermaphrodites or possess separate sexes " f. 



While these words were being published and read in 

 Germany, the English naturalist, Brightwell \, discovered 

 the small misshapen male of a Rotifer allied to Ehrenberg's 

 genus Notommata, previously altogether overlooked. This 

 was an epoch-making discovery, the importance of which 

 was immediately recognized by Dalrymple and further deve- 

 loped by him in a detailed special investigation. The last- 

 named naturalist furnished the proof that the male of Notom- 



* Translated by W. S. Dallas, F.L.S., from the ' Zeitschrift fin- wissen- 

 schaftliche Zoologie,' Band xli. pp. 226-251. 

 f Vergl. Anat. p. 184 (1848). 

 % Ann. & Mag. Nat. Hist. ser. 2, vol. ii. p. 153 (1848). 



Ann. & Mag. N. Hist. Ser. 5. Vol. xv. 10 



