Segregation, therefore, means that the gamete, or sex cell after maturition, has either dominant or recessive determiners, never both. Segregation thus affects the purity of the gametes. The matured ovum and spermatozoön are always pure, even in the hybrid plants or animals. Accordingly, when a spermatozoön, with a white determiner impregnates an ovum with a white determiner, although both originated in black hybrids, the zygote, or the impregnated cell, will be a pure white. When a black ovum is impregnated by a black spermatozoön, the zygote will be a pure black. If the ovum is black and the spermatozoön is white or the ovum is white and the spermatozoön is black, the zygote will also be black, but a black hybrid. Black + black = black, 25% pure. Black + white = black, 25% hybrid. White + black = black, 25% hybrid. White + white = white, 25% pure. Thus, when a black bean e. c. is crossed with a white bean, all the offspring in the first generation will be black but hybrids. When two of these hybrids are then crossed, the dominant color black will be represented by 75 per cent. of the offspring and the recessive color white by 25 per cent., i. e., the offspring in the second generation, although both parents are black, will be three-fourths black and one-fourth white. For the gamete of two hybrid parents is always pure. The zygote of two hybrid parents is either pure or hybrid. When the two gametes are similar, the zygote is pure and is called homozygous, when the two gametes are dissimilar, the zygote is heterozygous. Hybrids, by the faculty of segregation, produce in the first generation of hybridism, fifty per cent. homozygous zygotes (25% pure whites and 25% pure blacks) and fifty per cent. heterozygous zygotes (all hybrid blacks). Hence the apparent paradoxical phenomenon that when a pure blond is married to a pure brunette, all the children are brunette, while when both the parents are brunette, but hybrids, the offspring will be twenty-five per cent. blond and only seventy-five per cent. brunette. The blond being recessive can only be pure, while the brunette being dominant, may be either pure or hybrid. [Illustration: CUT XXIX. _Diagram illustrating the fertilization of the egg after Boveri._