Sturtevant crossed Columbian Wyandottes and Brown Leghorns. The F₁ sons were alike, whichever way the cross was made. They were fairly typical Wyandottes, which race carries therefore more of the dominant plumage characters (two or three?). There were two types of daughters, depending on the direction in which the cross was made. When the father is Wyandotte, the daughters are like him (except for stippling of the Leghorn type). When the father is Brown Leghorn the daughters are somewhat stippled red birds. In the former case the daughters getting their Z chromosome from their Wyandotte father resemble him; in the latter case the daughters getting their Z chromosome from their Leghorn father look more like him. Their failure to look exactly like him must be due to autosomal factors derived from the Wyandotte mother that dominate other autosomal factors from the father. Hagedoorn crossed Black Breasted Game bantams (like those used in my Sebright crosses) to Brown-Breasted bantams. In the latter the black breast feathers of the male are bordered by lemon; the hens are nearly black. Black-breasted male to “brown-red” female gave both black-breasted sons and daughters. In the reciprocal cross all the sons were black-breasted (like the mother) and all the daughters were brown red like the father. Evidently the factor here for Brown Breasted game is sex-linked and recessive. In this case the new mutant sex-linked character is recessive to the wild type. Davenport (1912) crossed Brown Leghorns to Dark Brahmas. In the cross and its reciprocal all the sons are alike. Two dominant sex-linked factors were found,[5] viz, the white background characteristic of the Dark Brahmas and the red upper wing-coverts (and back) characteristic of the Brown Leghorns. On the other hand, the _daughters_ differ in the two crosses, in each case resembling their father in their hackle color. When two sex-linked characters are involved in a cross it is possible to determine by suitable matings whether an interchange between the chromosomes that bear them has taken place. In the case of the sex chromosomes only one sex, the male, has both like chromosomes, viz, ZZ, and we expect from analogy with the _Drosophila_ work that crossing-over would be found between the sex chromosomes only in the male. Goodale has recently (1917) made the important discovery that in poultry crossing-over takes place between the sex chromosomes (ZZ) in the male, but not in the female (ZW or ZO). This relation, therefore, is the reverse in birds and flies, for, in the one, crossing-over takes place in the female and in the other in the male. Whether this difference extends also to the other chromosomes in birds as it does in flies is as yet not known.