OBSERVATIONS ON THE MATURATION STAGES OF 

 THE PARTHENOGENETIC AND SEXUAL EGGS 

 OF HYDATINA SENTA 



BY 



DAVID DAY WHITNEY 



I Introduction 137 



II Material and methods 138 



III Female egg 140 



rV Male egg 141 



V Winter egg 142 



VI General discussion 143 



VII Summary 144 



VIII Literature 145 



I INTRODUCTION 



Despite the experiments that have been carried out by several 

 workers to discover how sex is determined in parthenogenetic 

 eggs the attempts to show that such external factors as tempera- 

 ture or food influence the result do not appear to have been suc- 

 cessful. Attention has turned more recently to the possibihty 

 that there are internal factors in the eggs that are all-important 

 in producing males or females. 



As early as 1845 Dzierzon brought forward very strong evidence 

 to show that the eggs of the honey-bee, Apis mellifica, always 

 develop into males if unfertilized, but if fertilized they develop 

 into females (queens or workers). In other words, internal rather 

 than external agents bring about the result. This theory has been 

 often attacked and strongly defended, and now seems to be 

 generally accepted. 



In the aphids Balbiani and Stevens find that the same female 

 may produce both male parthenogenetic and fertihzed or winter 

 eggs. Lauterborn finds the same phenomenon in the Rotifer, 

 Asplanchna, and Issakowitsch in a Daphnid. Whether the eggs 

 that are fertilized are originally male eggs or develop from a dif- 



The Journal of Experimental Zoology, vol. vi, no. i. 



