154 THE AMERICAN NATURALIST [Vol. L 



The last space shows that 3.7 per cent, of these off- 

 spring were less than two thirds the normal size. This 

 again compares unfavorably with the other combinations, 

 and here also the individuals born one in a litter show a 

 superiority over those born in litters of two. 



From a consideration of this table it may be concluded 

 that the vigor of a guinea pig varies inversely with the 

 size of the litter in which the animal is produced, and this 

 is equally true whether the animal is born from normal 

 or alcoholic parentage. However, the differences be- 

 tween the mortality of animals born in litters of one, two 

 or three from normal parentage are not nearly so great 

 as comparable differences between the members of the 

 small and large litters from alcoholic lineage. For ex- 

 ample, the difference in mortality between normal ani- 

 mals in litters of one or two is about 1 per cent., or 

 scarcely any; between these and the mortality of speci- 

 mens born three in a litter there is a difference in mor- 

 tality record of about 24 per cent., to the discredit of the 

 larger litters. 



The comparable differences in the alcoholic lines is ever 

 so much greater. There is almost 14 per cent, higher 

 mortality among individuals from litters of two than 

 from litters of one, and actually about 43 per cent, higher 

 mortality among animals from litters of three than from 

 litters of one. The difference between the mortality per- 

 centages in the litters of one and the litters of two from 

 alcoholic inbred animals is 50 per cent. In other words, 

 the mortality is three times as high among individuals 

 from litters of two as from litters of one in inbred alco- 

 holics, while the normal individuals born in litters of two 

 are equally as good as those in litters of one. The par- 

 ents from the injured alcoholic lines are incapable of pro- 

 ducing large litters of strong individuals. The sub- 

 normal fetus fares pretty well alone in the uterus but is 

 put at a great disadvantage by having to divide its uter- 

 ine nourishment with brothers and sisters. 



Another almost equally plausible explanation of this 



