146 CHARLES R. STOCKARD AND GEORGE N. PAPANICOLAOU 



the productivity of the different Unes. The numbers 1 to 5 in- 

 dicate the number of young, one, two, three, four, or five 

 produced by a female in a single litter. Litters of five indi- 

 viduals are the largest that have occurred from this strain of 

 guinea-pigs. The average number of young in a litter from the 

 normal lines is 2.77, and of the 233 animals included in this 

 column 24.03 per cent of them were born in litters of one or 

 two young. About 39 per cent were born in litters of three, 

 while 37.33 per cent of the animals were members of large litters 

 of four and five individuals. There were only a few normal in- 

 bred animals, as shown in the third column, but their general 

 occurrence in the different-size litters was about as in the straight 

 normal lines, half of the animals were born in litters of three, 

 and almost 30 per cent in larger litters, and only about 20 per 

 cent in litters smaller than three. The average litter happens 

 to be in the small number of inbred animals a little higher than 

 in non-inbred stock. 



The arrangement of the young in large and small litters in the 

 alcoholic and alcoholic inbred lines is almost exactly the re- 

 verse of what we have just seen for the normal. Again, a little 

 less than half of the animals occur in litters of three. But over 

 30 per cent of the individuals are from litters of only one or two, 

 while about 20 per cent are born in litters of four or five. Stated 

 in other words, in the normal lines one and one-half times as 

 many individuals are born in litters of four or five as in litters of 

 one or two, while in the alcoholic lines one and one-half times as 

 many are born in litters of one or two as in litters of four or five. 



The explanation of this, we believe, is as follows: About half 

 of the pregnancies in this stock of guinea-pigs should result in 

 litters of three, as is found to be the case in all of the lines of 

 table 1. All litters of less than three young are due in the first 

 place to a low productivity on the part of the female as is prob- 

 ably indicated by the production of more than one-fifth of the 

 normal young in such litters. In the second place, small lit- 

 ters are frequently due, particularly in the alcoholic lines, to the 

 death and absorption ih utero or early abortion of one or more 

 members of an originally large litter. The absorption in utero 

 of such embryos, often of rather large size, may occur in a nor- 



