140 SEX INHERITANCE 



reduction divisions is supressed when a worker's 

 egg gives rise to a female. Such a supposition 

 finds some support in the fact that in other groups 

 of Hymenoptera (saw flies and gall flies) females 

 arise regularly from unfertilized eggs. In some of 

 the species of gall flies, males are unknown; in 

 others they appear very rarely. 



The female of Dinophilus apatris produces large 

 and small eggs in equal numbers. From the former 

 arise females, from the latter males (Korschelt, 

 von Malsen, Shearer, Nachtsheim). The small eggs 

 may predominate in some of the earlier laid batches, 

 so that at this time sons are in excess, but if the 

 mother remains alive, so that the full output is 

 produced, the sex-ratio becomes 1 to 1 (Nachtsheim) . 

 If the mother dies early, there may appear an excess 

 of males. What factor determines whether an egg 

 is to become a large female-producing egg, or a 

 small male-producing egg is not knowTi. The sug- 

 gestion, that the difference in size is due to the 

 number of yolk-bearing cells that are absorbed by 

 the egg during its gro^\"th period, has been disproven 

 by Nachtsheim; for he finds at the end of that 

 period that all the eggs are of the same size and the 

 difference in their size comes in later. 



lO 



