No. 599] SHORTER ARTICLES AND DISCUSSION 699 



was the problem of intraracial correlation with which Alexander 

 Graham Bell 3 was dealing when he studied the fertility of the 

 multi-nippled race of sheep at Beinn Bhreagh. 



Notwithstanding the simplicity of the biological problem a cer- 

 tain amount of confusion seems to have arisen. Thus Parker 

 and Bullard (loc. cit.) state: 



It is the chief object of our paper to discuss the relation of the size 

 of litters to the number of nipples in the domesticated swine, Sus 

 scrofa Linn. 



But instead of determining the correlation between the num- 

 ber of teats of the sow and the number of her young they have 

 actually calculated the relationship between the number of sib- 

 lings in the litter in which a pig was born and the number of 

 nipples which she herself possesses! Surely it should not require 

 specialization in animal behavior to convince one that the teats 

 which are of real service to a young pig are not its own, but those 

 of its mother ! 



Pearl 4 has quite correctly determined the correlation between 

 the number of nipples in the individual mothers and the number 

 of young in their litters. This he finds to be very low, 6 r = 0.195 

 ± .086. 



It is rather difficult to agree with Pearl in his statement that 



It would seem, a priori, that natural selection should have operated 

 to bring about a high correlation, both intra- and inter-racial between 

 these two variables, size of litter and number of mammae in the dam. 



There seems no reason whatever to suppose that natural selec- 

 tion would tend to produce a correlation between the number of 

 mammae in the mother and the size of her litters within a race, 

 providing it has produced an average number of 7iipples suffi- 



3 Bell, Alexander Graham, Science, N. S., 9: 637-639, pi. 5, 1899; loc. cit., 

 19: 767-768, 1904; loc. cit., 36: 378-384, 1912. 



4 Pearl, E., "On the Correlation between Number of Mammaj of the Bam 

 and Size of Litter in Mammals. EL Intraracial Correlation in Swine," 

 Proc. Soc. Exp. Biol. Med., 11: 31-32, 1913. 



5 Wentworth (Jour. Agr. Bes., 5: 1148, 1916) records another very low 

 coefficient on unpublished data, but does not state specifically whether it is 



as in Pearl's series, or between the number in a litter (weighted with their 

 own number) and number of nipples in the individual pigs, as in the series 

 of Parker and Bullard. 



