404 



PROCEEDINGS OF THE AMERICAN ACADEMY. 



In the pigs studied by Wentworth (1913, p. 269) the mode, which is 

 even more marked than in our series, fell upon 10, instead of 12, a 

 difference probably due to a difference in breeds. 



Plotting the records contained in Table 3 in the form of a frequency 

 polygon. Table 4, it is clear that the groups representing even numbers 

 of nipples stand relatively high as compared with those representing 

 odd numbers, a condition which indicates that the arrangement of 

 nipples tends to be in pairs. This is also evident from the table given 

 for Duroc Jersey swine by Wentworth (1913, p. 2G9), who has shown 

 that the nipples are more probably inherited in pairs than laterally. 



TABLE 4. 



Frequency Polygon showing the Distribution of 5970 Pigs (1000 Litters) 



According to the Number of Nipples on each Pig. The Numbers 



OF Nipples are Plotted as Abscissae and the Number of Variates 



AS Ordinates (Table 3). 



300 



IG 



Numbers of 7ii2)ples in male and female pigs. The numerical dis- 

 tribution of the nipples in male and in female pigs is given in Table 5. 



In the 3024 male pigs the nipples ranged from 9 to 18, with a mean 

 number of 12.4+ and a mode of 12. the standard deviation was 0.6906 

 =fc .0060. In the 2946 female pigs the nipples ranged from 8 to 18 with 

 a mean of 11.9+ and a mode of 12. The standard deviation was 



