2O6 GEORGE W. TANNREUTHER. 



ovary is replaced by the testis. In some forms, however, like 

 Rhino ps vitrea, the male possesses all of the above mentioned 

 points and does not show any indication of degeneration. In 

 other forms as in Polyarthra platyptera, the male rotifer resembles 

 a vorticella detached from its stem. Why degeneration is 

 carried much farther in some species than in others is rather a 

 puzzling problem. In Asplanchnia ebbesbornii, the varying de- 

 grees of degeneration are greater than in any previously reported 

 species. Without the presence of the few actively free-swimming 

 males, and more especially a knowledge of their embryonic 

 development, the extremely degenerate males (B, 15 and Fig. 7, 

 m.e.i] would in all probability remain unknown. It would not 

 at all be surprising, if in some of the groups where males have 

 not been reported, that extremely degenerate or parasitic males 

 exist as described above. 



COLUMBIA, Mo., 

 April 30, 1919. 



LITERATURE CITED. 

 Hudson, C. T., and Gosse, P. H. 



'89 The Rotifera or Wheel-Animalcules. Two vols. London. 

 Jennings, H. S. 



'95 The Early Development of Asplanchnia Herricki. Bull. Mus. Comp. 



Zool. Harvard. 

 '02 Rotatoria of the U. S., II. A Monograph}- of the Ratulida;. Bull. M. S. 



Fish Comm. 



Rousselet, C. F. 



'97 On the Male of Rhinops ritrea. Journ. R. Mic. Soc., Vol. 17. 

 Shull, F. A. 



'10 Studies in the Life Cycle of Hyil/ilhia senta. I., Artificial Control of the 

 Transition from Parthenogenetic to the Sexual Method of Reproduction. 

 Journ. Exp. Zool., Vol. S. 

 Tannreuther, Geo. W. 



The Development of Asplanchnia ebbesbornii (Rotifer). Journ. Morph., 

 Manuscript in press. 



Whitney, D. D. 



'10 The Influence of External Conditions upon the Life Cycle of Hydalina 



'nta. Science, X.S., Vol. 32, no. 819, Sept. 9. 

 Zelinka, C. 



'92 Studien uber Radertiere, III. Zeitschr. fur Wis. Zool., Vol. 53. 



