CHAPTEE XV 

 THE FACTORS WHICH DETERMINE SEX^ 



" What was a question once is a question still." — BACO^f. 



A WORK upon the Physiology of Eeproduction would be incomplete 

 without some reference to the problem! of sex-determination, and 

 some account of the more recent attempts which have been made 

 towards its solution. The question has been dealt with q,t length 

 in several recent works, such as those by Morgan and by Doncaster, 

 Correns and Goldsehmidt, and Goldschmidt,^ and the reader is 

 referred to these treatises, especially the last, for further references 

 and fuller information in regard to certain of the points discussed. 

 It is hoped, however, that the present summary may prove useful if 

 only as a supplement to the other volumes that have appeared, 

 since certain important papers dealing with sex-determination and 

 containing an account of experimental investigations have been 

 published since the appearance of the works referred to, and these 

 papers I have endeavoured to summarise here. Moreover, some of 

 the more recent observations, and more particularly those relating 

 to sex reversal, have necessitated a further revision of the conclusions 

 previously arrived at. 



Eeproduction in organisms may occur by simple fission or 

 budding, in which case it is said to be asexual, or it may involve 

 the union of two conjugating cells, which in Metazoa and Metaphyta 

 are specially differentiated for the purpose, and are known as ova 

 and spermatozoa (see Child's work, p. 2^5, above). In some animals 

 these two types of cell are produced by the same individual, which 

 is then said to be hermaphrodite or monoecious, but such a condition 

 is rare or absent altogether among the highest forms of life. In 

 the vast majority of animals there are two sexes — that is to say, 

 two kinds of sexual individuals, the male and the female, whose 



' With additions by Cresswell Shearer. 



2 Morgan, Heredity and Sex, New York, 1913. Doncaster, The Determination 

 of Sex, Cambridge, 1914. Correns and Goldsehmidt, i5ie Verm-hung und Bestim- 

 mung des Oeschlechts, Berlin, 1913. Goldsehmidt, Mechanismus und Fhysiologie 

 der 'OesoMechtsbestimmwng, Berlin, 1920. See also Geddes and Thomson, The 

 Evolution of Sex, Eevised Edition, London, 1904; Thomson, iTerei^^, London, 

 1914 ; and Babcock and Clausen, Genetics wi Relation to Agriculture, New York, 

 1918. 



