412 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



TABLE 14. 



Superimposed Frequency Polygons Illustrating the Distribution of 



THE Numbers of Pigs in Litters (Left) and the Numbers of 



Nipples on the Females (Right). The Numbers of Pigs 



AND OF Nipples are Plotted as Abscissae and the 



Numbers of Variates as Ordinates. 



10 11 12 13 11 15 16 17 



Summary. 



1. 1000 litters of unborn pigs contained 5790 individuals; the 

 mean number of pigs per litter was 5.97, the mode 6. 



2. Of the 5790 pigs, 3024 were males and 2946 were females; 

 there were 102.6+ males for every 100 females. 



3. In the whole population the nipples ranged from 8 to 18 with a 

 mean of 12.2+ and a mode of 12. 



4. In the male pigs the nipples ranged from 9 to 18 with a mean of 

 12.4+ and a mode of 12, and a standard deviation of 0.6906 ± 

 .0060; in the females the range was from 8 to 18 with a mean of 11.9+, 

 a mode of 12, and a standard deviation of 0.7905 =>= .0069. 



5. On the left side the nipples ranged from 4 to 9 with a mean of 

 6.1 — , and a mode of 6; on the right side they ranged from 4 to 10 

 with a mean of 6.1 — , and a mode of 6. The coefficient of correlation 

 for the two sides was 0.6063 =•= .0055. 



6. In the whole population the arrangement of the nipples fell 

 under the regular plan (p. 402) in 3559 cases and under the irregular 

 plan in 2411 cases. 



7. There is no obvious relation between the size of the litter and 

 the number of nipples in the females. Though there may be as few 

 nipples as 8 and as large litters as 15, disadvantageous combinations 

 of large litters borne by females with few nipples cannot be of frequent 

 occurrence. Commonly there are about twice as many nipples, 12, 

 as young, 6. 



