PARKER AND BULLARD. — LITTERS AND NIPPLES IN SWINE. 405 



0.7905 ± .0069. Thus the females are over 14 percent more variable 

 than the males. 



The similarity in the numbers of nipples in the males and in the 

 females, as exliibited in Table 5, is noteworthy. When it is considered 

 that the mammary glands, so far as is known, are only normally 

 functional in the females and probably never have been functional in 

 the males, even in the most primitive mammals, it is remarkable that 

 the two sexes in pigs should at the outset of life show such considerable 



TABLE 5. 



Pigs from 1000 Litters, 3024 IMales and 2946 Females, Classified Ac- 

 cording TO THE Number of Nipples on each Pig. 



similarity. The presence of embryonic nipples and the other rudi- 

 ments of the mammary apparatus in male mammals must be depend- 

 ent upon a continual process of inheritance from the female side, a 

 process which is apparently the outcome of high female specialization, 

 whereby traits which have arisen in that sex are, so to speak, forced 

 upon the other. The result is that an organ functionless both in the 

 past history and the present state of a sex is nevertheless continuously 

 exliibited by that sex. 



Numbers of nipples on right and left sides. The numbers of nipples 

 on the right and on the left sides of pigs are recorded in Table 6. 



The nipples on the left side range from 4 to 9 with a mean number of 

 6.1 — and a mode of 6, and on the right side from 4 to 10 with a mean of 

 6.1+ and a mode of 6. This striking similarity is also shown in the 

 percent of individuals in which the two sides agree in numbers, or 



