If, again, two heterozygous birds be mated, the variability is still greater and the proportion of clean-footed offspring rises to 12 per cent. These, together with some of the extremely slightly booted offspring, represent the extracted dominants. The whole range now falls into three regions divided by the middle of grades 2 and 5. These regions correspond to the DD's, the DR's, and the RR's of typical cases of segregation, and their relative proportions are approximately as 25: 50: 25. Finally, if a heterozygote be mated to an extracted dominant the proportion of clean-footed offspring rises to about 30 per cent and the whole range of variation falls readily into two parts, the one comprising grades 0 and 1, the other grades 2 and above. The first includes the DD offspring; the second, the DR's; and their frequency is equal. One will not fail to note that we are not here dealing with a case of blending simply, and the inheritance of the blend; such a view is negatived by the fact of the much greater variability of DR × DR cross over the simple D × R cross of the first generation. One may safely conclude, then, that, despite the apparent blending of booting characters in the first generation of hybrids, true segregation takes place. But this is always to be seen through the veil of imperfect dominance. A casual examination of table 38 would seem to show a correlation between the grade of booting of the parents and that of the average of their progeny. Thus, on the whole, the parental grades run high in the upper part of the table and run low in the lower part. This relation would thus seem to confirm Castle's conclusion for polydactylism in guinea-pigs that there is an inheritance of the degree of a character. One consequence of such an inheritance would be that it would be possible in a few generations to increase or diminish the grade of a character and fix any required grade in the germ-plasm. A more careful consideration of the facts of the case shows that this relation has another interpretation. The grade of boot of the different parents varies largely because their gametic constitution is diverse. As table 39 shows, the parents of the upper part of table 38 are chiefly extracted recessives, and consequently their booting and that of their offspring are characterized by high grades. On the other hand, the parents of the lower part of the table are heterozygous or extracted dominants and, consequently, their grades and also those of their offspring average low. On account of the lack of homogeneity of the families in table 38, one can draw from it no proper conclusions as to relation between parental and filial grades. On the other hand, from a homogeneous table, like table 39, we can hope to reach a conclusion as to the existence of such a relation. I have calculated, in the usual biometric fashion, the coefficient of correlation between average parental and filial grades, and found it to be -0.17 ± 0.13. This can only be interpreted