400 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



The diita for this hivestigation were collected from litters of unborn 

 but nearly mature pigs that were available at one of the large slaughter- 

 ing establishments in Cambridge, Massachusetts. The sows from 

 which these litters were obtained, came chiefly from the corn-belt 

 of the Mississippi Valley and were in general about two years old. 

 They Avere of various breeds. Each set of records was taken from the 

 contents of a single uterus. On opening the uterus, the number of 

 pigs and their relative position in each horn was recorded, as well as 

 the sex of each pig and the number and arrangement of its nipples. 

 In all 1000 litters were examined, the records of which are given in an 

 appendix at the end of this paper. We are under obligations to Mr. 

 H. D. Fish for assistance in calculating and checking the results. 



In dealing with the relation of the size of the litter to the number of 

 nipples, we shall take up, first, the composition of the litters, then the 

 number and arrangement of the nipples, and, finally, a comparison 

 of the numbers of young in the litters with the numbers of nipples 

 in the females. 



Composition of the Litters. 



Numbers of pigs in a litter. As already stated, the total number of 

 litters that we examined was 1000, and the number of pigs in a litter 

 varied from 1 to 15. The maximum number of 20 in a litter, as as- 

 sumed by Aristotle (1SS3, p. 164), or any excess of that number, as 

 noted by Gilbert White (1870, p. 222), was not met with by us. The 

 frequency with which litters of different numbers occurred is given 

 in Table 1. 



TABLE 1. 



A THOUSAND Litters classified according to the Number of Pigs in each. 



Since the thousand litters contained in all 5970 pigs, the mean 

 number of pigs per litter is 5.97 which is very close to the mode, 6, 

 as shown in Table 1. These numbers are smaller than those given by 

 Surface (1909), who found litters of Poland China pigs to vary from 



