STUDIES ON THE ROTIFER ASPLANCHNIA EBBES- 

 BORNII, WITH SPECIAL REFERENCE TO 



THE MALE. 



GEORGE W. TANNREUTHER, 

 ZOOLOGICAL LABORATORY, UNIVERSITY OF MISSOURI. 



INTRODUCTION. 



The rotifers were collected in small rain pools, placed in 

 aquaria with tap water and kept in the laboratory at room 

 temperature, free from direct sunlight. The age of the cultures, 

 when the present work was begun, varied from four months to 

 two years. The rotifers appeared in the different cultures at 

 regular intervals of about six to eight weeks. 



The life cycle of Asplanchnia is as follows: females hatch from 

 the resting or fertilized eggs. These females (first generation) 

 produce parthenogenetically twenty to thirty offspring, which 

 are likewise females. The latter reproduce parthenogenetically. 

 All of the offspring of one parent, being either all females or 

 males. Thus the females of the second generation may be called 

 male producers or female producers. The life cycle of Hydatina 

 senta as described by Shull, in most respects corresponds to the 

 above description. 



When the males become sexually mature, impregnation of 

 the male-producing females occurs, and the impregnated females 

 produce resting eggs instead of males or both resting eggs and 

 males. The resting egg stage terminates the active pe'riod of 

 each cycle and carries the rotifers to the beginning of the active 

 period of the next following cycle. The active free-swimming 

 period of each cycle continues from two to three weeks. The 

 inactive or resting egg stage of each cycle varies from five to 

 eight weeks. If impregnation of the male producers is prevented, 

 no resting eggs are formed and the females continue to form males 

 parthenogenetically. 



If we consider the females that actually produce males the 

 sum total of all male producing females formed, the percentage 



194 



