CONCLUSION 509 



that they differ in respect to their metabolic processes," or, again, 

 " Upon what conditions within the fertilised egg does the sexual 

 differentiation depend ? In some way, we may now be reason- 

 ably sure, upon the physiological reactions of nucleus and 

 protoplasm." 



ii. Conclusion 



In conclusion, our view is that the difference between an 

 ovum-producer and a sperm-producer is fundamentally a differ- 

 ence in the balance of chemical changes, i.e. in the ratio of ana- 

 bolic and katabolic processes, which may, of course, have its 

 structural expression in the relation of nucleoplasm and cyto- 

 plasm. Nor do we leave this difference in metabolism-rhythm 

 as a mere vague phrase, for we see its analogue in the contrast 

 between the ovum and the spermatozoon (though it is quite 

 unwarrantable to think of these as being in themselves respec- 

 tively female and male cells), between the macrogamete and the 

 microgamete, between the encysted and the flagellate cell, 

 between the plant and the animal, and in many a familiar con- 

 trast all through the series of Organisata. We adhere, in short, 

 to the thesis of The Evolution of Sex, that the sex-difference 

 is but one expression of a fundamental alternative in variation, 

 to be seen throughout the world of life. This view finds strong 

 experimental confirmation in Baltzer's investigations on the plas- 

 ticity of sex-conditions in Bonellia according to the nurture, in 

 Geoffrey Smith's study of the constitutional consequences of 

 parasitic castration in crabs, and in Riddle's work on the control 

 of sex in pigeons. 



