THE FACTORS WHICH DETERMINE SEX 651 



are all gradations between true and partial hermaphroditism 

 (in which the essential organs of reproduction are not involved), 

 and between the latter and the completely unisexual condition, 

 in which the characters of the other sex are either latent or^ 

 absent altogether. 



Complete hermaphroditism is the normal state in many 

 groups of invertebrate animals (many sponges, ccelenterates, and 

 worms, and some molluscs and crustaceans). In some forms the 

 male and female sexual elements do not exist contemporaneously, 

 but are called forth separately by different environmental con- 

 ditions or are associated with particular phases in the repro- 

 ductive cycle (see Chapter I.). In such cases the fact that the 

 animal is hermaphrodite is liable to be obscured. 



Among vertebrate animals true hermaphroditism is rare, 

 though its casual occurrence has been recorded even in 

 Mammalia, and is said to be comparatively frequent in 

 certain species of Amphibia. 1 



According to Castle 2 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 



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. 

 Cf. Weber's finch (p. 313), which was a lateral gynandromorph. Such 

 gynandromorphs are not uncommon among some insects (Hymenoptera). 

 See also Shattock and Seligmann's papers quoted on p. 315. For an 

 exhaustive account of the question of hermaphroditism in Man, with a 

 full discussion of the evidence, see von Neugebaur, Hermaphroditismus 

 beim Menschen, Leipzig, 1908. 2 Castle, loc. cit. 



