34 HELEN DEAN KING 



probable error of the mean exclude the possibility that the sex 

 ratios could have been produced by chance or by environmental 

 action. The results, therefore, do not support the contention 

 that the male is the chief factov in determining the sex ratio in 

 the rat. 



The sex ratio in each of the three groups of litters obtained by 

 the mating of stock females with males from various generations 

 of the two inbred series was below the norm, whether the sire of 

 of the litters belonged in the A or the B series. The sex ratio 

 in the group of litters sired by males from the A series (102.3 cf : 

 100 9 ) was only 6 points higher than that in the litters sired 

 by males from the B series (96.2 o^ : 100 9 ). The results in this 

 case, therefore, do not indicate that inbreeding, with .selection, 

 influenced the potency of the spermatozoa in any way ; they seem 

 rather to signify that the particular stock females used for breed- 

 ing tended to attract spermatozoa that were 'female-producing' 

 rather than those that were ^male-producing.' 



The results of the various experiments in which inbred and out- 

 bred animals were paired, taken in connection with those from 

 the experiments in which matings were made between litter 

 brother and sister, seem to show that in the rat, as in Drosophila 

 (Moenkhaus) , the female has a greater influence than the male in 

 determining the sex ratio, and that chance alone cannot be the 

 factor that determines whether an egg shall be fertilized by a 

 'male-producing' or by a 'female-producing' spermatozoon. 



The size of the probable error of the mean (tables 6 and 7) in- 

 dicates that in each series the difference between the sex ratio for 

 the group of inbred litters and that for the group of half -inbred 

 litters is a significant one. Apparently, therefore, the chemo- 

 tactic reaction between the ovum and the spermatozoon is not 

 quite the same where these sexual elements come from unrelated 

 individuals as when they are produced by individuals that are 

 closely inbred. A somewhat analogous case is found in the her- 

 maphroditic ascidian, Ciona, where normally, as Castle ('96) and 

 Morgan ('04, '05) have shown, the eggs are not fertilized by sper- 

 matozoa from the same individual, although they are readily fer- 

 tilized by spermatozoa from any other individual, while the 



