In Mendelian experiments, a heterozygote individual is one arising from gametes containing opposite members of a pair of characters, in other words, from the union of a gamete carrying a dominant with another carrying a recessive. A pure recessive individual is one arising from the union of two gametes both carrying recessives. If a heterozygote is bred with a pure recessive the offspring are half heterozygote and half recessive. The heterozygote individual in typical cases shows the dominant character. In the formation of its gametes when the reduction division of the chromosomes takes place, half of them receive the dominant character, half the recessive. When the division in the gametes of the recessive individual takes place its gametes all contain the recessive character. Thus, if we indicate the dominant character by _D_ and the recessive by _d_, the constitution of the two individuals is _Dd_ and _dd_. The gametes they produce are _D+d_ and _d+d_, and the fertilisations are therefore _Dd_, _Dd_, _dd_, _dd_, or heterozygote dominants and pure recessives in equal numbers. It is evident that the reproduction of the sexes is very similar to this. One of the remarkable facts about sex is that, although the uniting gametes are male and female yet they give rise to males and females in equal numbers. If one sex were a dominant this would be in accordance with Mendelian theory. In accordance with the view that the dominant is something present which is absent in the recessive, the Mendelian theory of sex assumes that femaleness is dominant, and that maleness is the absence of femaleness, the absence of something which makes the individual female. If we represent the character of femaleness by _F_ and maleness or the recessive by _f_, we have the ordinary sexual union represented by _Ff_x_ff_; the gametes will then be _F_+_f_ and _f_+_f_ and the fertilisations _Ff_ and _ff_, or males and females in equal numbers, as they are, at least approximately, in fact.