HEEEDITY 



the gametes themselves, it being supposed that 

 early or late fertilization of the egg might 

 influence its sex. Experimental evidence, how- 

 ever, as to these several hypotheses is wholly 

 negative, when one eliminates other possible 

 factors from the experiment. Everything 

 points to the conclusion that sex rests in the 

 last analysis upon gametic differentiation, just 

 as the color of a guinea-pig in a mixed race 

 of blacks and whites depends upon whether the 

 gametes which unite to produce it carry black 

 or white. As the heterozygous black guinea- 

 pig forms black-producing and white-producing 

 gametes in equal numbers, so there is reason 

 to think male-producing and female-producing 

 gametes are formed in equal numbers by the 

 parent, in many cases at least. But is it not 

 possible that there may exist individuals which 

 produce the two sorts of gametes in unequal 

 numbers, and so would have a tendency to 

 produce more offspring of one sex than of the 

 other! Perhaps so, though we have no evi- 

 dence that such a condition, if it does exist, is 

 transmitted from one generation to another. 

 On this point I made experimental observa- 



154 



