Dffrniinuifioi! of Sex in Hydafnia Senta 25 



about twenty-three, provided that there had been no more mothers 

 of fertihzed eggs to have been produced. The Diagram 3 shows 

 only one occurring between the eighteenth and twenty-seventh 



The number and order of occurrence of the mothers of fertilized 

 eggs together with the number and occurrence of the layers of 

 male eggs in parallel sets of daughter-females seem to indicate 

 that the layer of male eggs and the layers of fertilized or winter 

 eggs are identical at one stage of their life. 



In another species of rotifer, Asplancha,Lauterborn has observed 

 winter eggs and male embryos in the same individual. Among 

 the Daphnia, Issakowitsch has found that the same lemale may 

 produce winter eggs and male eggs. 



Therefore it is not unreasonable to suppose that the immature 

 male-laying female of Hydatina senta is capable of developing 

 into a layer of fertilized eggs or a layer of male eggs, according 

 to the impregnation or lack of impregnation by the male. 



IX SUMMARY 



1 Temperature has no influence in determining the sex of 

 Hydatina senta. 



2 About 22 per cent of the females at any temperature from 

 14° to 29° C. are male-laying. 



3 A male-laying female produces eggs faster than a female- 

 laying female and at a temperature of 25° to 29° C. a male-lay- 

 ing female produces more eggs throughout her lifetime than a 

 female-laying female. 



4 The male-laying iemales occur in the early part of a family 

 (it daughter-females. 



5 Starving the young females for the first few hours after they 

 hatch does not cause them to produce a higher percentage of male 



eggs. 



6 There are no strains that constantly produce a high or a 

 low percentage of male-laying females. 



7 The "pure female-laying female strain" can give rise to the 

 normal percentage, 22 ±, of male-laying females. 



