THE FACTORS WHICH DETERMINE SEX 689 



its casual occurrence has been recorded even in Mammalia, and is 

 said to be comparatively frequent in certain species of Amphibia.^ 



According to Castle ^ the true hermaphrodite is a sex mosaic, the 

 alternative sexual characters existing side by side without dominance 

 of either, and passing (without segregation) into the gametes. 

 Dioecious individuals are supposed to result ordinarily from a union 

 of gametes in which one sex is dominant and the other recessive, so 

 that no one individual is purely either male or female. The occurrence 

 of partial hermaphroditism may be held to be an expression of an 

 incomplete dominance of the characters of one sex. 



Partial hermaphroditism is usually said to occur when only one 

 kind of gonad is developed (either testis or ovary) in conjunction 

 with accessory generative organs characteristic of 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 hermaphroditism.^ 



Among animals which are usually regarded as purely dioecious 

 there are many instances of vestigial or even of functional sexual 



1 See Geddes and Thomson, loc. cit. Curtis; " Studies on the Physiology of 

 Reproduction in the Domestic Fowl " {Biol. Bull., vol. xvii., 1909). Pearl and 

 Surface have described a case of an hermaphrodite fowl which had a testis 

 on one side and an ovary on the other. . The accessory organs were likewise 

 unilaterally arranged. Externally it was an antero-posterior gynandromorph, 

 having male characters in front but female body characters. Gf. Weber's 

 chaffinch (p. 337) and Poll's bullfinch, which were lateral gynandromorphs. 

 Such gynandromorphs are not uncommon among some insects (JSymenoptera). 

 See also Shattock and Seligmann's papers quoted on p. 341, and Bateson and 

 Thomas, "Note on a Pheasant showing Abnormal Sex Characters," Jour, of 

 Genetics, vol. vi., 1917. For an account of the question of hermaphroditism in 

 man, with a discussion of the evidence, see von Neugebaur, Hermaphroditismus 

 beim Menschen, Leipzig, 1908, and Gudernatsch, " Hermaphroditismus Verus in 

 Man," Amer. Jour, of Anat, vol. xi., 1911. The latter author states that there 

 is no clear case of true hermaphroditism in man or any mammal. 



^ Castle, loc. cit. 



' Lillie's interpretation of the Free-Martin is referred to below (p. 695). 

 According to Berry Hart, however, the Free-Martin is in reality a sterile bull 

 which is co-twin of a normal fertile bull (" The Structure of the Reproductive 

 Organs of the Free-Martin, with a Theory of the Significance of the Abnor- 

 mality," 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 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. It has been shown, however, by Lillie that the twins arise 

 from two separate ova. 



