THE EFFECT OF THE CHEMICAL COMPOSITION OF 



THE MEDIUM ON THE LIFE CYCLE OF 



HYDATINA SENTA^ 



A. FRANKLIN SHULL 



(Department of Zoölogy, Columbia University.) 



Page 

 I. Introduction 174 



II. Description of the experiments 175 



1. Influence of substances introduced with the food on the percentage 



of male-producers 175 



2. Influence of various iindetermined constitnents of feces on the 



percentage of male-producers 177 



3. Influence of alkalinity on the percentage of male-producers .... 182 



4. Influence of urea on the percentage of male-producers 184 



5. Influence of ammonium Compounds on the percentage of male- 



producers 184 



6. Influence of beef-extract on the percentage of male-producers . . 186 



7. Influence of creatin on the percentage of male-producers 189 



III. Summary and conclusions 190 



IV. Bibliography 193 



I. INTRODUCTION 



In several groiips of animals there is a more or less regulär 

 alternation of parthenogenetic with sexual reproduction. A num- 

 ber of generations may be produced parthenogenetically, after 

 which females appear that produce eggs requiring fertilization. 

 Or parthenogenetic and sexual females may occur in varying pro- 

 portions in the same generation. For one of these groups, the 

 suborder Cladocera of the phyllopod Crustacea, commonly called 

 " daphnians," the Suggestion has several times been made that the 

 chemical composition of the water in which the animals lived 

 might affect the transition from one mode of reproduction to the 

 other, but no very clear evidence has been adduced. In another 

 group, the rotifers, in which a similar alternation of methods of 

 reproduction exists, although no one has heretofore suggested that 



^ The major portion of the results here presented has been published in The 

 Journal of Experimental Zoology, 1910, viii, pp. 311-354, and 191 1, x, pp. 1 17-166. 



174 



