192 CHARLES R. STOCKARD AND GEORGE N. PAPANICOLAOU 



272 males was 9513 grams; that for the 136 females was 4654 

 grams. If this total weight be doubled for comparison with the 

 total weight of the double number of males, we have 9308 

 grams. The males again have a total advantage, amounting 

 here to 205 grams. The average excess weight of the males is 

 0.75 gram^ or a 1.08 per cent excess weight of males over 

 females. 



It will be noted in this table that the average weight of the 

 individuals is very low. This is due to the fact that a number of 

 abortions in which the sex could be distinguished, as well as 

 premature still-births are included. These small specimens 

 have brought the average in some cases almost below the birth 

 weight which permits survival. It is also noticed that the 272 

 males in the second line only weigh about one-quarter more 

 than the 105 males in the first line of the table, and this is due 

 to the fact that there were many more abortions and early pre- 

 mature births of litters consisting of three individuals than of 

 two. While the males in the litters of one male and one female 

 averaged almost 75 grams, the males in litters of two males and 

 one female averaged less than 35 grams. 



The third line of the table shows 125 litters of one male and 

 two females. The 125 males weighed 4428 grams which may be 

 doubled to give 8856 grams for comparison with the total weight 

 of 8790 for the 250 females. There is a total advantage of 66 

 grams in favor of the males. The average excess of male weight 

 is 0.26 gram, or 0.37 per cent over female weight. 



The last case of thirty-six litters, consisting of two males and 

 two females each, gives a total excess of 85.5 grams to the males. 

 The average excess weight of the males over females is 1.19 

 grams, and the per cent of excess of males over females is 1.87. 



It is thus seen that the males born in litters consisting of 

 both sexes possess a superiority in body weight over the females in 

 every combination. We do not attribute this constant excess in 

 favor of the males to a sexual dimorphism in size. In a group 

 of guinea-pigs both young and adult females are often larger in 

 size than comparable males, and no constant size difference be- 

 tween the two sexes is known. It seems more probable that 



