TWINNING IN RUMINANTS 99 



From this and other statements it is clear that Hart 

 considered the freemartin and its twin male as deriva- 

 tives of a single fertilized egg (monozygotic). On this 

 assumption, which is not well founded, as we shall sec 

 later, he builds up a hypothesis to explain how the 

 freemartin arises, which may be briefly summed up as 

 follows: Thus the freemartin with a potent bull-twin is 

 the result of the division of a male zygote, so that the 

 somatic determinants are equally divided, the genital 

 determinants unequally divided, the potent going to 

 the one twin, the potent bull, the non-potent genital 

 determinants going to the freemartin. The potent 

 organs are dominant, the non-potent recessive. The 

 Mendelian scheme may be figured as follows: 



Male sex gamete X Female sex gamete 



Male zygote 



which if it twins 



may give 



D 



R 



F' 



F" 



Bull with equivalent Bull with equivalent 



soma and potent soma and non-jwtent 1 



genital organs organs (female type) | 



This MendeUan view of the freemartin as a pure 

 or extracted recessive lacking its genital determinants 

 is one of the oddest developments of the neo- ■Mendelian 

 cult and might be discussed pro and con at some 

 length were it not for the fact that the whole h>pothesis 

 is based on an error, for bovine twins arc not monozygotic. 



It will be noted that while the earlier workers con- 

 sidered the freemartin as a hermaphrodite, Hart con- 

 siders it a recessive or non-potent male, co-zygotic with 



