ACTION OF SEX HORMONES IN FOETAL LIFE 375 



often been found. This observation is of interest in connection 

 with the problem stated in footnote 5, p. 389. 



The theoretical interpretation of the free-martin must be 

 based on one of two assumptions, either (1) that it and its part- 

 ner, are identical, i.e., monozygotic twins, or (2) that they are 

 fraternal, i.e., dizygotic twins. Under the first assumption, as 

 the sex of monozygotic twins is undoubtedly identical, the free- 

 martin would necessarily be interpreted as a modified male. 

 Under the second assumption it would be almost equally a mat- 

 ter of necessity to interpret the free-martin as a female, for there 

 is no possibility that the association of two males in utero should 

 cause the transformation of one of them into a free-martin. On 

 the first assumption the explanation of the modification must be 

 found in the twdnning process itself, i.e., in the division of the 

 single zygote that ex hyp. formed the two twins. But on the 

 second assumption no one has hitherto attempted to explain 

 how the association of male and female in utero could lead to 

 sterility of the female with a more or less pronounced male or- 

 ganization of the internal organs of reproduction, nor why cer- 

 tain females should escape the defect, nor why the phenomenon 

 should be peculiar to cattle. It is, therefore, natural that the 

 first assumption should have been the one followed in all pre- 

 vious theoretical interpretation of the free-martin, and that it 

 formed the working hypothesis wdth which my own work began. 



The first theoretical view that we shall consider is that of 

 Spiegelberg ('61) who said of cattle twins: "If the twins are 

 both female or of opposite sex, the organs of reproduction are 

 as a rule well formed; if they are both male, it very frequently 

 happens that one of them is an hermaphrodite." This conclu- 

 sion was based on the examination of two pairs of different 

 sexed twins in cattle ; he made anatomical examination of the 

 free-martins and found one of them a normal female, but in the 

 other the female internal organs of reproduction were mostly 

 absent, and w^ere replaced by rudimentary seminal vesicles, 

 rudimentary vasa deferentia, and a rudimentary gonad on one 

 side which he interpreted as probably a small testis with more or 

 less separated epididymis. The internal organs were accepted 



