EFFECTS OF INBREEDING ON THE SEX RATIO 33 



cases I can see no valid objection to the assumption that the 

 cheniotactic reaction between ova and spermatozoa may be even 

 more deHcate and thus, under given conditions, make possible 

 the fertilization of an egg by a spermatozoon that has one sex 

 potency rather than the other. 



There is another possible interpretation of the anomalous sex 

 ratios found in the inbred litters of the two series. We might 

 assume that inbreeding had acted on the males in some way so as 

 to render one kind of spermatozoon more potent than the other in 

 fertilizing the ova, and that this difference in potency came to 

 have an heritable basis in the germ plasm and so could be acted 

 upon by selection. In the A series of inbreds, according to this 

 assumption, the 'male-producing' spermatozoa became the more 

 potent; in the B series the 'female-producing' spermatozoa came 

 to have the greater potency. Were this assumption correct it 

 should receive confirmation both from the results of the experi- 

 ments in which inbred females were paired with stock males and 

 from the experiments in which stock females were paired with 

 males from different generations of the two inbred series. The 

 litters obtained in the former case should show a nearly equal 

 proportion of the sexes (provided it was merely a matter of chance 

 which kind of spermatozoa fertilized the ova), since the males 

 were outbred and therefore, theoretically, the two kinds of sper- 

 matozoa had equal power to fertilize the ova. In the latter case 

 the litters obtained should show a high sex ratio when the sire 

 came from the A series of inbreds and a low sex ratio when the 

 sire belonged to the B series. 



As shown in table 4 and in table 5, the half -inbred litters pro- 

 duced by the mating of inbred females with stock males gave sex 

 ratios that were very far from equality. In only one generation 

 of each series was there an approximately equal proportion of the 

 sexes, in all other cases the variation was in a definite direction: 

 in the A series there was an excess of males; in the B series the 

 females predominated. In both series, moreover, the sex ratios 

 in the half-inbred litters were much closer to those in the cor- 

 responding inbred litters than they were to the norm. The uni- 

 formity in the various series of records and the small size of the 



THE JOURNAL OF EXPERIMENTAL ZOOLOGY, VOL. 27, NO. 1 



