No. 557] INHERITANCE OF MAMMJE IN SWINE 



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highest numbers of mammae, would incline the writer to 

 believe that the rudimentary mammae of the scrotum and 

 thigh are independent of the abdominal series, and 

 furthermore that the Mendelian interpretation is correct. 



Conclusions. — I. There are two common sorts of varia- 

 tion from the even paired type in the mammae of swine, 

 aside from the simple addition and subtraction of pairs. 

 These are the "triangle" and "suppressed" nipple vari- 

 ations. Each shows a definite tendency to reproduce 

 itself in the offspring, but both are apparently associated 

 with an increased number of pairs. 



II. The seat of the greatest variation in the animals 

 under discussion is the second pair of mamma?. This is 

 perhaps due to the type of variation in the sires. 



III. There is apparently a breed difference in regard 

 to the number of mammae. Bateson shows that in Tam- 

 worths and Berkshires, 13, 14 and 15 mammae are typical, 

 occurring in 77 per cent, of the cases. The Duroc Jerseys 

 studied show in 90 per cent, of the animals, 10, 11 or 12 

 mammae. 



IV. The ratio of asymmetrical to symmetrical patterns 

 increases as the number of mammae increase. With five 

 pairs symmetry is almost constant ; with six pairs, sym- 

 metry and asymmetry are equal. With seven pairs 

 asymmetry outnumbers symmetry 2 to 1. 



V. No evidence definitely showed that asymmetry is 

 unilateral in inheritance. Asymmetry on one side of the 

 parent does not, on the average, produce asymmetry on 

 the same side only of the offspring. 



VI. Sows differing in number of mammae, when mated 

 with the same boar, produce offspring variable in number 

 of mammae. In general, sows with a large number of 

 mammae produce more offspring of a corresponding sort 

 than do sows with a small number of mammae. The differ- 

 ence, however, is not great, and neither sort apparently 

 breeds true. The correlation of mother and offspring in 

 number of mamma* is measured by the coefficient .2626 ± 

 .028. 



