MODIFICATION OF THE GERM-CELLS IN MAMMALS 



191 



sex-ratio is very high and yet the late male mortality is higher 

 than that for the females. The total mortality for the females 

 is higher than that of the males, 31.71 per cent against 29.68 

 per cent. It is further shown below the table that small litters 

 have a higher sex-ratio than large litters, the sex-ratios for litters 

 of one and two young being respectively 113.1 and 114.8. While 

 for litters of three and four young the sex ratios are 101.7 and 

 106.6. It has been pointed out before that the small litters are 

 often due to an early prenatal mortality which has destroyed 

 some of the original members, and since the sex-ratios of such 

 litters are high the majority of embryos dying may have been 

 females. We may see finally by a study of table 7 that female 

 animals are generally smaller at birth than males in the same 

 litter, and as their total higher mortality would indicate, they 

 are probably also weaker. 



TABLE Vll 



THL BIKTH WL16HTS OF MALE AND FEMALE MLMBERSOFAMXED UTTEK5 



Table 7 only includes mixed Utters; that is, those containing 

 both male and female members. It shows that in 105 litters of 

 two animals of opposite sex the total birth weight of the 105 

 males was 7861 grams and of the 105 females only 7525 grams, 

 or 336 grams less. The average excess weight of males over 

 females in these litters of two was 3.2 grams, giving a percent- 

 age of excess weight of 2.18 in favor of the males. 



One hundred and thirty-six litters of three, consisting of two 

 males and one female, are recorded. The total weight of the 



