Mamm^ and Size of Litter. 



3i 



17 (834) 



On the correlation between number of mammae of the dam and 

 size of litter in mammals. II. Intraracial correlation in swine. 



By Raymond Pearl. 



[From the Biological Laboratory of the Maine Agricultural 

 Experiment Station.] 1 



The data here discussed regarding the intraracial correlation 

 between mamma number and size of litter in Duroc Jersey swine 

 were furnished me by Professor E. N. Wentworth, formerly of the 

 Iowa State College. I take this opportunity of expressing my 

 appreciation of this kindness. The material was collected in the 

 course of Professor Wentworth's studies on the inheritance of 

 mamma number. 2 In the case of 13 out of the 57 dams recorded 

 data are available for the size of two successive litters, namely 

 those of 191 1 and 1912. In these cases, in order to avoid unequally 

 weighting the table because of the fertility of the dams, each dam 

 has been entered in Table I once only, the litter size entered being 

 the mean of the two successive litters. 



The ungrouped data are given in Table I. 



TABLE I. 



Showing the Intraracial Correlation Surface for the Variables (a) Number 

 of Mamm/E of Dam, and (6) Size of Litter, in Swine. 



Mammae of Dam. 



Size of Litter. 



Totals. 



1 



2 



3 



4 



5 



6 



7 



8 



9 



10 



11 



12 



13 





10 

 II 

 12 

 13 

 14 



I 





I 



I 



I 



2 



3 



1 



S 



3 

 1 



4 



2 

 I 



4 



4 



3 

 1 



3 

 2 

 4 



I 



3 



1 



18 

 8 

 24 



5 













1 











3 









2 



Totals 



1 



0 



I 



1 



I 



6 



6 



8 



7 



8 



13 



1 



3 



1 



57 



In dealing with this table slightly different methods were used 

 than in the case of the interracial correlation. 3 The classes of 

 both variables have been assumed to center at the points given by 



1 Paper No. 53. 



2 American Naturalist, Vol. XLVII, pp. 257-279, 1913. 

 8 Cf. thesj Proceedings, Vol. X, p. 31, 1913. 



