ACTION OF SEX HORMONES IN FOETAL LIFE 377 



maintains, it can hardly be classed as a non-potent part of the 

 genital tract, i.e., by definition undeveloped parts of the opposite 

 sex, nor can the vasa deferentia of the free-martin be so classed; 

 nor yet the external genital parts which are usually pure female. 

 The theory moreover implies that as the free-martin receives the 

 'non-potent' genital parts, the bull twin must lack them, and 

 must continue to propagate male individuals lacking them, for 

 neither of which deductions is there the slightest evidence, or 

 any attempt to produce evidence. Finally, there is not any at- 

 tempt to explain why the twinning process should be attended' 

 by such extraordinary results in cattle, and involve nothmg of 

 the kind in other mammals. Hart notes that the theory im- 

 plies the possibility of a similar defect in the twinning of a female 

 zygote, and he refers to Numan's case cited before (footnote 2) 

 as an example. 



Bateson ('13, pp. 44-45) also attempts an explanation of the 

 free-martin on the basis that it is co-zygotic with its twin. 



For it is impossible to suppose that mere development in juxtaposi- 

 tion can produce a change of this character. It is conceivable that we 

 should interpret it by reference to the phenomenon of gynandromor- 

 phism, seen occasionally in insects, and also in birds as a gi-eat rarity. 

 In the gjiiandromorph one side of the body is male, the other female. 

 A Ijullfinch for instance has been described with a sharp line of di\4sion 

 down the breast between the red feathers of the cock on one side and the 

 brown feathers of the hen on the other. In such cases neither side is 

 sexually perfect. If the halves of such a gynandromorph came apart, 

 perhaps one would be a free-martin. 



The interpretations of Hart and Bateson are based on the theory 

 that the free-martin and its twin are monozygotic, and they in- 

 volve the conclusion that the free-martin is derived from a male 

 zygote. They may be called anatomical interpretations be- 

 cause they are based exclusively on anatomical evidence. Cole 

 has also come to the same conclusion on statistical grounds, 

 which I discuss in the second part (pp. 380). 



The literature on this subject is scanty, and it would serve no 

 good purpose to continue with the few incidental citations that 

 might still be made. Embryological e\ddence that would alone 

 give a basis for correct interpretation has been entirely lacking; 



