CHAPTER XXIV 
THE DETERMINATION OF SEX 
Introduction: the Different 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 Drelin- 
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 Drelin- 
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 Drelincourt 
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.’ 
1 One or even two polar bodies are given off 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. 
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