THE FACTORS WHICH DETERMINE SEX 657 



is merely one factor in a complex system of causes), and that 

 the physiological mode of thought requires one to associate the 

 characters of an organism with its particular metabolism and 

 not with any special sort of cell substance. 1 



GENERAL CONCLUSIONS 



If it be true that all individuals are potentially bisexual 

 (one of the two sexes being recessive or latent excepting in 

 hermaphrodites), and that changed circumstances, leading to a 

 changed metabolism, may, in exceptional cases, even in adult 

 life, cause the development of the recessive characteristics (as 

 in the case of the Crustaceans mentioned above), it would seem 

 extremely probable that the dominance of one set of sexual 

 characters over the other may be determined in some cases at 

 an early stage of development in response to a stimulus which 

 may be either internal or external. The observations which 

 Smith and others have made upon certain Crustaceans point 

 even to the possibility that sex may be reversed after it has 

 once been established. 



It seems certain that sex is not determined by the same 

 factors in all cases, neither is it determined at the same period 

 of development. It may well be that some gametes have an 

 initial tendency to give rise to males and others to give rise to 

 females, and to this extent it is probably legitimate to speak 

 of male and female ova or male and female spermatozoa. 2 More- 

 over, the conclusion is probably correct that these are developed 

 (at least generally) in simple Mendelian ratios. But it is also 

 probable that no gamete is either purely male or purely female, 

 and it is possible that in some the two kinds of sexual determi- 

 nants or tendencies are about equally represented. 



1 The presence of a certain kind of cell substance must of course influence 

 the metabolism, but the extent of its influence will depend upon other factors, 

 and may vary with different external conditions. 



2 Bateson and Punnett suggest that in some forms of life (e.g. Verte- 

 brates) the ova are the sexually differentiated gametes, and that in other 

 organisms (e.g. Crustaceans) the sexual differentiation occurs among the 

 spermatozoa. Guyer's cytological observations, however (p. 635), seem to 

 show that male Vertebrates may be sexually heterozygous. Moreover, 

 Baltzer's cytological observations seem to show that among sea-urchins there 

 may be two kinds of eggs (Arch. f. Zellforsch., vol. iv., 1909). 



2T 



