TWINNING IN RUMINANTS loi 



of Hart, an,d cites certain statistical evidence in favor of 

 it. As the abstract is so brief it may be quoted in full: 



A study of 303 multiple births in cattle, obtained directly 

 from the breeders. The records include: 43 cases homosesaial 

 male, 165 cases recorded heterosexual (male and female), 88 cases 

 homosexual female, 7 cases triplets, a ratio of twins approx- 

 imately 1:4:2 instead of i : 2 : i expected, if there were 

 no disturbing element entering in. The expectation may be 

 brought more nearly into harmony with the facts if it is assumed 

 that in addition to ordinary fraternal (dizygotic) twins there are 

 numbers of "identical" (monozygotic) twins of both sexes, and 

 that while in the case of females those are both normal, in the 

 cases of a dividing male zygote, to form two individuals, in one 

 of them the sexual organs remain in the undifferentiated stage, 

 so that the animal superficially resembles a female and is ordi- 

 narily recorded as such, although it is barren. The records of 

 monozygotic twins accordingly go to increase the homosexual 

 female and the heterosexual classes, while the homosexual male 

 class, in which part of them really belong, does not receive any 

 increment. This brings the expected ratio much nearer the 

 ratio obtained. 



Any female calf twinned with a male is referred to as a 

 freemartin. According to the interpretation given, some free- 

 martins should be fertile while others are sterile. It was found 

 that both exist. 



It will be noted that Cole interprets the freemartin 

 as an undeveloped male in which the sex-organs remain 

 in the undifferentiated state and thus resemble those 

 of a juvenile female. This view of the freemartin as 

 a male is a concession to the idea that monozygotic 

 twins should be of the same sex, since sex is supposed 

 to be determined at the time of fertilization. 



As is always the case when expectations are 

 based on incomplete data, these numerous divergent 



