STUDIES IN THE LIFE CYCLE OF HYDATINA SENTA 



II. THE ROLE OF TEMPERATURE OF THE CHEMICAL COMPOSITION 

 OF THE 'medium, AND OF INTERNAL FACTORS UPON THE 

 RATIO OF PARTHENOGENETIC TO SEXUAL FORMS^ 



A. FRANKLIN SHULL 



Department of Zoology, Columbia University 



Introduction 117 



Problem and method " 118 



Experiments with external factors 120 



Influence of temperature on the percentage of male-producers 120 



Influence of various undetermined constituents of feces on the percentage 



of male-producers 123 



Influence of alkalinity on the percentage of male-producers 129 



Influence of urea on the percentage of male-producers 132 



Influence of ammonium compounds on the percentage of male-producers . . 132 



Influence of beef -extract on the percentage of male-producers 135 



Influence of creatin on the percentage of male-producers 137 



Experiments with internal factors 140 



Discussion 152 



Summary 164 



Bibliography 165 



INTRODUCTION 



In two earlier papers (ShuU, '10a and '10b) I have discussed 

 the influence of environment upon the transition from the parthe- 

 nogenetic to the sexual mode of reproduction in Hydatina"'^ senta. 



1 I desire to thank Prof. E. B. Wilson for the use of laboratory facilities at Cold 

 Spring Harbor, Long Island, where much of the work described in this and my 

 former paper was done. 



' It has been pointed out to me by several zoologists independently that the name 

 Hydatina can not stand as a genus of rotifers, that name having been previously 

 used for a mollusk. 



