Phenomenon of Sex 
of the male or the female sex. A vast amount 
of ingenuity has been expended by zoologists in 
the attempt to ascertain what it is that deter- 
mines sex. Many theories have been advanced, 
but no one of them has obtained anything like 
general acceptance, because its opponents are 
able to adduce facts which appear to be incom- 
patible with it. 
It is tempting to try to interpret the pheno- 
menon of sex on the assumption that the female- 
producing biological molecule or unit is an 
isomeride of the male-producing cell. Certain 
facts, however, seem to negative the idea, as, for 
example, the occasional appearance in an indi- 
vidual of one sex of characteristics of the other 
Sex. 
Possibly the attempts to explain the pheno- 
mena of sex-production on a Mendelian basis 
may prove to be more successful. It seems not 
impossible that each fertilised egg contains 
material which is capable of developing into 
male generative organs and material which is 
capable of developing into female generative 
organs, but that only one kind of material, that 
which dominates, succeeds in developing. The 
number of what are known as “ X-elements” 
that happen to be present in the fertilised egg 
appear to decide which kind of material is to be 
dominant. 
But the problem of the determination of sex, 
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