Determination of Sex in Hydatina senta 



23 



If a large number, 45 + per cent, of the daughter-females of 

 one mother produce males it does not necessarily follow that a 

 high or a low percentage of the daughter-females of the next gen- 

 eration will produce males. Nor does it seem to be true that if 

 the daughter-females of one generation produce all female off- 

 spring that the daughter-females of the following generation will 

 do so. Table XXII shows the history of both classes of daughter- 

 females in five generations. 



TABLE XXII 



Record of all the female-laying females that were isolated in five consecutive generations, showing 

 that there is no constant relationship between the percentage of male-laying females that are produced 

 by a mother and the percentage of male-laying females that are produced by the daughter-female in 

 the nest generation. 



Gen. 



Sisters 



III 



IV 



16 



36 



45 

 42 



4^ 



47 



41 

 36 



40 

 26 



VIII THE PRODUCTION OF FERTILIZED EGGS 



The winter or fertilized egg is supposed to be the male partheno- 

 genetic egg which has been fertilized. This produces a female. 

 The egg has much more yolk material and a thicker shell than the 

 male parthenogenetic egg. A female produces from twelve to 

 twenty fertilized eggs, while a male-laying female produces from 

 forty to fifty parthenogenetic eggs. In order to obtain fertilized 

 eggs males must copulate with very young male-laying females. 



