400 



L. DONCASTER 



zygotes in such familios are female, whether the egg-nuclei 

 before fertilization contain always twenty-seven chromosomes, 

 or sometimes twenty-eight. 



Evidence that All-female Families are not Caused 

 BY Non-viability of Male Zygotes. 



In the earlier papers a number of families were recorded in 

 which considerably over half the eggs were reared either to 

 imagines or to larvae in which the sex was definitely deter- 

 minable, but there still seemed some slight chance that all- 

 female families might arise through death of male zygotes 

 at an early age. This, however, seems to be definitely excluded 

 by the results of later experiments, as is shown in Table I, 

 which gives a list of the all-female, or almost exclusively 

 female families in which at least two-thirds of the eggs were 

 reared to larvae or adults of ascertainable sex. 



Family, 



Table I. 

 Number of Eggs. Eggs Hatched. 



97 

 31 



110 



82 

 1 1 

 not recorded 



Larvae or Imagines. 



46 



22 

 56 



? 



66 

 28 

 77 

 66 

 54 

 28 

 37 

 58 



9 

 45 

 42 

 22 

 39 



o^ 

 1 



In view of the fact that in most cases almost all the eggs 

 hatch, and that as soon as the larvae are old enough to be 

 dissected the sex is already clearly distinguishable, these results 

 make it practically indubitable that the all-female families 

 do not arise in consequence of the death of male eggs or larvae. 

 But the matter can be tested in another wav,^ which makes 

 this conclusion doubly sure. 



' It seems as though a paragraph has been omitted here, but there is no 



