690 THE PHYSIOLOGY OF REPRODUCTION 



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 floridcr), in 

 which the male possesses a marsupium which acts functionally as a 

 placenta. 1 



In the great crested grebe the positions assumed during pairing 

 by the two sexes are interchangeable, for the .male may adopt the 

 passive attitude and the female the active one. 2 Keversal of pairing 

 positions has also been described in moor hens and in tame pigeons. 

 Here we have an instance of the reversal of an instinct. 



Weininger 3 has elaborated the idea that just as there may be an 

 " Idioplasm " that is the bearer of the specific characters, whether 

 morphological, physiological, or psychological, and exists in all the 

 cells of a multicellular animal, so also there may be two sexual modes 

 in which this idioplasm can appear, namely an " Arrhenoplasm " or 

 male plasm, and a " Thelyplasm " or female plasm. He maintained 

 further that every metazoon cell (and not merely every reproductive 

 cell) has a sexuality lying somewhere between arrhenoplasm and 

 thelyplasm, but that the actual degree of maleness or femaleness 

 varies in the different groups of cells of which the animal is built up. 

 Moreover, the different parts of the organism were supposed to possess 

 their own sexual determinants, which were believed to be stable 

 from their earliest embryonic foundation. Weininger made no 

 suggestion as to what it is that determines the differentiation of the 

 original protoplasm into arrhenoplasm and thelyplasm, but his idea, 

 though somewhat too morphologically conceived, is useful if only 

 because it emphasises the fact that male and female characters coexist 

 (though they are very unequally represented) in most if not in all 

 dioecious individuals that is to say, that such individuals are rarely, 

 if ever, wholly male or wholly female. " There may be conceived," 

 he wrote, " for every cell all conditions, from complete masculinity 

 through stages of diminishing masculinity to its complete absence 

 and the consequent presence of uniform femininity." 



Weininger drew special attention to the gradations in sexual 

 characters which exist among men and women. There are many 

 men, he remarks, with a poor growth of beard and a weak muscular 

 development, who are otherwise typically males ; and so also there 



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

 Pipe-Fish, Siphostoma floridce," Proc. U.S. Nat. Jfus., vol. xxix., 1905. 



2 Julian Huxley, " The Courtship Habits of the Great Crested Grebe, :i Proc. 

 Zool. Soc., 1914. Huxley discusses the significance of the process, of which he 

 gives a detailed account. References are given to papers by Selous ( 

 1901-02), also describing reversed pairing in the grebe and other birds. 



3 Weininger, Sex and Character, English Translation, London, 1906. 



