No. 557] INHERITANCE OF MAMM2E IN SW 



numbers among the swine studied is shown 

 ing table : 



Per cent, frequency i Q. 7S 38.31 2«.o2 24. 95 I 6.48 | 2.95 



Nearly 90 per cent (89.8) of the pigs bear ten, eleven or 

 twelve mammae, and may therefore be considered the 

 normal types of the Duroc Jersey. In Bateson's data on 

 Tamworth's and cross-bred Berkshires in his "Materials 

 for the Study of Variation, " he finds that twelve is the 

 lowest number of mammae occurring, fourteen is the mode 

 and seventy-seven per cent, fall on thirteen, fourteen and 

 fifteen. His numbers are much smaller (35), but it is 

 highly probable that there is a difference in breeds as 

 regards number of mammae, particularly between those 

 of bacon and lard type. 



Correlation of Number of Mamma between Bams and 

 Pigs. — The coefficient of correlation for number of mam- 

 mae between the sows and pigs was not high (.2626 ± 

 .028), yet it showed distinct inheritance. There was ap- 

 parently no difference due to sex, as the boar pigs showed 

 a correlation of .1734 ± .04 to their mothers, and the sow 

 pigs were only slightly greater, .2133 ± .04. Since with 

 the probable errors in consideration the two coefficients 

 overlap, it seems doubtful if sex makes any difference in 

 the inheritance. 



Evidence of Segregation in Number of Mamma— The 

 sows of the first generation were plotted against their 

 grand-daughters giving the following results. 



