DETERMINATION OF SEX IN HYDATINA SENTA 



DAVID DAY WHITNEY 



I Introduction i 



II Material and methods 3 



III Influence of temperature 4 



1 Maupas' experiments 4 



2 Author's experiments 5 



a Temperature 20° to 22° C 5 



h Temperature 25° to 29° C 8 



c Temperature 14° to 1 5° C 9 



rV The relative number of eggs which a male-laying female and a female-laying female produce 10 



1 Temperature 20° to 22° C 11 



2 Temperature 24° to 29° C n 



V Early production of male-laying females in a family of daughter-females 13 



VI Influence of food 15 



1 Temperature 20° to 22° C 16 



2 Temperature 14° to 15° C 18 



3 Temperature 25° to 26° C 18 



« VII Male and female strains 19 



VIII Production of fertilized eggs 23 



IX Summary 25 



I INTRODUCTION 



On account of the supposed influence of external factors in 

 determining sex in Hydatina senta, this rotifer has attracted much 

 interest in recent years. As is well known Hydatina produces 

 three kinds of eggs, viz: (i) parthenogenetic eggs which develop 

 into females; (2) smaller parthenogenetic eggs which develop into 

 males; and (3) fertilized eggs which develop into females. Each 

 female produces only one of these three kinds of eggs. Thus 

 three types of females may be distinguished, viz: (i) females 

 which produce females parthenogenetically, or female-laying 

 females, 9 9 ; (2) females which produce males parthenogeneti- 

 cally, or male-laying females, d* 9 ; and (3) the sexual females 

 that lay fertilized eggs. 



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



