THE PARASITIC WASP, HADROBRACON BREVICORNIS. 43 



has been shown to occur in several groups. Such "male-pro- 

 ducing" species are called arrenotokous and it has been supposed 

 that all males arise from unfertilized eggs, females from fertilized. 

 This theory bears the name of Dzierzon (1845) who first applied 

 it to the honey-bee. The males produced by mated females are 

 assumed to develop from eggs into which spermatozoa have not 

 penetrated. Cytological observations showing that males of 

 several arrenotokous species are haploid, while females are 

 diploid tend to corroborate the theory derived from breeding 

 tests. 



The only published experimental work on arrenotokous forms 

 showing the method of inheritance of any character difference, 

 other than that of sex, appears to be in crosses of different races 

 of honey-bees. "Criss-cross" inheritance is the rule; the males 

 resemble the mother, while the females inherit characters from 

 both parents. Cross-bred females produce drones showing segre- 

 gation in expected one to one ratio. From the similarity of these 

 phenomena to sex-linkage, this method of inheritance may be 

 called sex-Unkoid. 



PRESENTATION OF DATA. 



(a) Black-eyed Stocks. The results in reference to sex-deter- 

 mination published in my previous paper (1918) showed that 

 the stock of Hadrobracon brevieornis obtained in Philadelphia at 

 that time was arrenotokous. The data may be briefly sum- 

 marized as follows: 



Sixty-one females set with males produced 683 males and 918 

 females. 



Nine females set with males produced 197 males, no females. 



Thirty-six virgin females produced 1,133 males, no females. 



Impaternate sons were crossed back to their virgin mothers 

 and in this way closely inbred daughters were obtained. 



Another stock of Hadrobracon was secured in Philadelphia in 

 December, 1917, and three virgin females were isolated, producing 

 in all 244 males. One of these females was later mated to one of 

 her sons and produced 9 males and 3 females. 



Three males and one female were caught in MifBintown, 

 Pennsylvania, May, 1920. From eggs laid by this female there 



