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 see 

 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 

 Mendehan scheme may be figured as follows: 



Male sex gamete X Female sex gamete 



Male zygote 



which if it twins 



may give 



Bull with equivalent 



soma and potent 



genital organs 



Bull with equivalent 

 soma and non-potent 

 organs (female type) 



This Mendelian 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 hypothesis 

 is based on an error, for bovine twins are 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 



