I02 THE BIOLOGY OF TWINS 



interpretations as to the nature and mode of origin of 

 the freemartin are all quite mistaken; now that we have 

 the problem really cleared up they seem almost equally 

 absurd. The MendeHan interpretation of Hart, the 

 suggestion involving gynandromorphism of Bateson, 

 and the inferences of Cole based on sex-ratios appear 

 alike far-fetched in the light of further facts and more 

 reliable conclusions. 



Recently F. R. Lillie' has solved the mystery of the 

 freemartin through an embryological study of twinning 

 in cattle. The material has been collected during the 

 past two or three years, and I have been much interested 

 in the progress of the research. LilHe's prehminary 

 paper was called forth as a reply to Cole's report just 

 given; he criticizes Cole's data and his interpretations, 

 and says: 



I wish to point out the fatal objection that, according to the 

 hypothesis, the females remaining in the heterosexual class are 

 normal; in other words, on this hjrpothesis, the ratio of normal 

 freemartins (females co-twin with a bull) to sterile ones is 3 : i ; 

 and the ratio would not be very different on any basis of 

 division of the heterosexual class that would help out the 

 sex-ratio. Hitherto there have been no data from which the 

 ratio of normal to sterile freemartins could be computed, and 

 Cole furnishes none. I have records of 21 cases statistically 

 homogeneous, three of which are normal and 18 abnormal. That 

 is, the ratio of normal to sterile freemartins is i : 6 instead of 

 3 : I- 



This ratio is not more adverse to the normals than might be 

 anticipated, for breeders' associations will not register freemartins 

 until- they have proved capable of breeding, and some breeders 

 hardly believe, in the existence of fertile freemartins, so rare are 

 they. 



■ F. R. LiUie, Science, N.S., XLIII (1916). 



