THE EFFECT OF A CENTRIFUGAL FORCE UPON 

 THE DEVELOPMENT AND SEX OF PARTHENO- 

 GENETIC EGGS OF HYDATINA SENTA 



DAVID DAY WHITNEY 



With One Plate 



I Introduction 125 



II Relation of the first cleavage plane to the stratification of the material of eggs centrifuged 



when the germinal vesicle is intact 126 



III Relation of the first cleavage plane to the stratification of the material of eggs centrifuged 



when the maturation spindle is present 127 



IV Condition of the young animals which developed from centrifuged eggs 128 



V The proportion of male and female producing females in the first, second and third gen- 

 erations after centrifuging 130 



VI General discussion 133 



VII Summary 134 



VIII Literature 135 



I. INTRODUCTION 



The eggs of Hydatina senta are very favorable for experiments 

 with the centrifugal machine. The adult females which contain 

 eggs in stages up to and including the first maturation spindle 

 may be centrifuged at the rate of twenty thousand revolutions in 

 two to three minutes without any apparent injury. The animal 

 is so transparent that the eggs can be seen immediately after cen- 

 trifuging and their condition recorded. The materials in the egg 

 are separated into three distinct zones, a pink zone, a middle clear 

 zone and a gray zone. This strat fied material only becomes 

 partly redistributed in the egg before cleavage and sometimes 

 scarcely any redistribution takes place. After the egg is laid 

 the polar body is formed and the first cleavage appears in thirty- 

 five vo forty-five minutes. The eggs develop within forty-eight 

 to seventy-two hours and produce in most cases normal embryos. 



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



