MODIFICATION OF THE GERM-CELLS IN MAMMALS 193 



this advantage in weight on the part of the males, the majority 

 of which are of alcoholic ancestry, is in line with the lower 

 mortality records of the males shown in the various columns of 

 table 6. And this may further bear on the explanation of the 

 high sex-ratios in those lines with high early mortalities or small 

 average litters. 



There is, therefore, much evidence to indicate that among 

 alcoholic guinea-pigs the females very probably suffer a much 

 higher early prenatal mortality than do the males, and it is 

 shown that the female mortality is higher than that of the males 

 at all other periods, table 6. 



Before proceeding further with our theoretical explanation of 

 the different sex-ratios in the several groups, which leads finally 

 to a consideration of views expressed in a previous communica- 

 tion, still another important relationship may be pointed out 

 between early prenatal mortality and the sex-ratio, on one 

 hand, and the late prenatal and postnatal mortality, combined in 

 table 6 under 'total dead,' on the other. Stated concisely, the 

 higher the sex-ratio and the early prenatal mortality, indicated 

 by the small average litter, the lower will be the total late pre- 

 natal and postnatal mortality, and vice versa. The columns 

 with the highest sex-ratios, 123.58 and 121.17, and at the same 

 time the highest early prenatal mortalities or the smallest aver- 

 age litters, 2.37 and 2.28, show the lowest late mortalities, 25.55 

 and 27.12 per cent. In the opposite way the columns with the 

 lowest sex-ratios, 96.8 and 86.51, and the lowest early prenatal 

 mortalities, or the largest average litters, 2.69 and 2.66, have the 

 highest later mortalities, 34.93 and 32.52 per cent. This is in 

 line with what was brought out during the discussion of table 4 

 showing that the higher the early prenatal mortahty, or the 

 smaller the average litter, the lower will be the late prenatal and 

 postnatal mortalities. 



There is one very evident objection to the foregoing explana- 

 tion of the peculiar sex-ratios as being due to a differential sex 

 mortality during the early prenatal periods. That is, among 

 the normal stock the sex-ratio is rather high, although the early 

 prenatal mortality is probably very low as indicated by the 



THE JOURNAL OF EXPERIMENTAL ZOOLOaY, VOL. 26, NO. 1 



