CHAPTER XXIV 



THE DETERMINATION OF SEX 



Introduction: the Dijj event Kinds of Sexual Individuals 



Few questions in biology have attracted more interest than 

 that of the determination of sex. Blumenbach, in his fascinating 

 brochure, " Ueber den Bildungstrieb," points out that Drehn- 

 court brought together two hundred and sixty-two groundless 

 hypotheses of sex that had been proposed, and Blumenbach 

 remarks quaintly that nothing is more certain than that Drehn- 

 court's own theory made the two hundred and sixty-third. In 

 recent years a large number of facts bearing on the determina- 

 tion of sex have been brought together, and yet the question 

 remains as much a puzzle as it was in the time of Drehncourt 

 and Blumenbach. 



Before attacking the main question of the determination of 

 sex let us consider the different kinds of sexual individuals found 

 in the animal kingdom. By sexual individuals we mean those 

 forms that reproduce themselves by eggs and sperm in contrast 

 to reproduction by budding, or by division, or by spores; but 

 while this distinction will hold in most cases, it is an arbitrary 

 distinction, since we recognize sexual reproduction in the pro- 

 tozoa, where entire individuals unite or even fuse, and the dis- 

 tinction between a spore and a parthenogenetic egg depends 

 largely upon what we suppose to have been the historic origin 

 of these two kinds of reproductive cells, rather than on any 

 inherent difference in the cells themselves.^ 



^ One or even two polar bodies are given ofif from parthenogenetic eggs, but 

 not from spores. The bearing of this difference on the sexual problem is un- 

 known. It is not necessarily connected with a reduction on the number of chromo- 

 somes. 



363 



