STUDIES IN THE LIFE CYCLE OF HYDATINA SENTA 



I. ARTIFICIAL CONTROL OF THE TRANSITION FROM THE 



PARTHENOGENETIC TO THE SEXUAL METHOD 



OF REPRODUCTION. 



AARON FRANKLIN SHULL 



Department oj Zoology, Columbia University 



With One Figure 



Introduction 



311 



Problem and methods -716 



Experiments 510 



Normal course of partheno gene tic series 510 



Variability of the percentage of male-producers in related strains under like conditions 320 



Influence of quantity of food culture on percentage of male-producers 320 



Influence of age of food culture on percentage of male producers 328 



Influence of substances in water on percentage of male-producers 330 



Influence of breeding from different parts of the family on percentage of male-producers 337 



Influence of size of family on percentage of male-producers 340 



Identity of sexual eggs and male eggs 342 



Summary of results 344 



Discussion 



345 



Bibliography 354 



INTRODUCTION 



In the attempt to solve the problem of sex determination, im- 

 portant experimental evidence supposed to bear on the question 

 has been derived from the rotifer Hydatina senta. It seems prob- 

 able, however, that the phenomena referred to in Hydatina 

 do not bear on sex-determination. It is practically certain that 

 the mother of the males is the sexual female. What at first seemed, 

 therefore, a question of sex-determination relates instead to the 

 transition from the parthenogenet;c to the sexual phase of the 

 life cycle, so that one could substitute the term sexual female for 

 the term male-producer in describing the phenomena. The 



