as the zygote is for one {129} or other or both of them in a homozygous or a heterozygous state. Moreover, certain of these intermediates will breed true to an intermediate condition of the pigmentation. A male of the constitution ffPPII when bred with females of the constitution FfPPIi will produce only males like itself and females like the maternal parent. We have dealt with this case in some detail, because the existence of families showing a series of intermediate stages between two characters has sometimes been brought forward in opposition to the view that the characters of organisms depend upon specific factors which are transmitted according to the Mendelian rule. But, as this case from poultry shows clearly, neither the existence of such a continuous series of intermediates, nor the fact that some of them may breed true to the intermediate condition, are incompatible with the Mendelian principle of segregation. [Illustration: FIG. 28. Diagram to illustrate the nature and composition of the F_2 generations arising from the cross of Silky hen with Brown Leghorn cock.] In connection with intermediates a more cogent objection to the Mendelian view is the case of the first cross between two definite varieties thenceforward breeding true. The case that will naturally occur to the reader is that of the mulatto, which results from the cross between the negro and the white. According to general opinion, these mulattos, of intermediate pigmentation, continue to produce mulattos. Unfortunately this interesting case has never been critically investigated, and the statement that the mulatto breeds true rests almost entirely upon {130} information that is general and often vague. It may be that the inheritance of skin pigmentation in this instance is a genuine exception to the normal rule, but at the same time it must not be forgotten that it may be one in which several interacting factors are concerned, and that the pure white and the pure black are the result of combinations which from their rarity are apt to be overlooked. But until we are in possession of accurate information it is impossible to pronounce definitely upon the nature of the inheritance in this case. [Illustration: FIG. 29. Pedigree of a family which originated from a cross between a Hindu and a European. Black signs denote individuals as dark as average Hindus. Plain signs denote quite-fair members, while those with a dot in the centre are intermediate.] {131}