652 THE PHYSIOLOGY OF REPRODUCTION 



both sexes. Such cases are by no means uncommon even among 

 the higher animals. The so-called " Free-Martins " among 

 cattle have been held to be examples of incomplete herma- 

 phroditism. According to Berry Hart, however, the Free- 

 Martin is in reality a sterile bull which is co-twin of a normal 

 fertile bull. 1 



Among animals which are usually regarded as purely 

 dioecious there are many instances of vestigial or even of func- 

 tional sexual organs characteristic of one sex being present 

 normally in individuals of the opposite sex. The mammary 

 glands and teats of the male mammal, and the clitoris of the 

 female are examples of such organs. A more striking case is 

 that of the pipe fish (Siphostoma florida.'), in which the male 

 possesses a marsupium which acts functionally as a placenta. 2 



Such cases as these have led Castle, Heape, and others to 

 conclude that all animals and plants are potentially herma- 

 phrodite, inasmuch as they contain the characters of both 

 sexes, although ordinarily the characters of one sex only are 

 developed, while those of the other are either latent or im- 

 perfectly developed. 



Castle has cited cases from among plants in which the 

 characters of one sex can be induced to appear by the artificial 

 destruction of those of the other. Examples of the same kind of 



1 Berry Hart, "The Structure of the Reproductive Organs of the Free- 

 Martin, with a Theory of the Significance of the Abnormality," Proc. Roy. 

 Soc. Edin., vol. xxx., 1910. The Free-Martin has also been regarded as a 

 sterile cow born co-twin with a potent bull. In most cases a vagina and 

 rudimentary uterus have been described, but vesiculae seminales and other 

 male organs are also stated commonly to occur. Berry Hart bases his 

 explanation of the occurrence of Free-Martins upon his recently elaborated 

 theory of sex. (Mendelian Action on Differentiated Sex, Edinburgh, 1909.) 

 According to this theory, sex is determined by a "sex-gamete" which 

 may be either male or female. There are also male and female " non- 

 sex gametes," which unite with the " sex-gametes " but are non-potent 

 in determining sex. A female sex-gamete uniting with a male non-sex 

 gamete gives rise to a female zygote, and conversely. Moreover, according 

 to Hart, a Free- Martin with a potent bull twin is the result of a division 

 of a male zygote, so that the somatic determinants are equally divided, 

 but the gametic determinants unequally divided, the potent going to the 

 one twin, the potent bull, and the non-potent to the Free-Martin. 



1 Gudger, " The Breeding Habits and the Segmentation of the Egg of 

 the Pipe-Fish, Siphoetoma Florida;," Proc. U. S. Nat. Mus., vol. xxix., 

 1905. 



