Sets of Conjugate Cycles of a Substitution Group.

2 Sumner, F. B., and Huestis, R. R., Genetics, Sept., 1921. 3 Almost nothing has been done in the way of hybridizing subspecies. But after all subspecies do not differ in any essential way from species. Whether or not two groups of mammals or birds are regarded as species or subspecies depends upon whether the intergrading forms have been preserved. The extremes are often more widely distinct than two "good" species. 4De Vries, H., Species and Varieties, Lecture IX. 6 Festskrift utgiven av Lunds Universitet, 2, No. 8, 1918 (1-145). 6 Genetics, July, 1921. 7 I will not say of factors, since this mode of expression would concede the universality of the factorial scheme of heredity, a view which I regard as quite unproved at present. 8 J. Genetics, Feb., 1920, July, 1920. 9 July, 1920, p. 82.-It should be noted that the uniformity last referred to is not a uniformity of the F2 generation as a whole, but a uniformity of the melanic individuals within that generation. 10 Carnegie Institution, Publ., No. 205, 1914. 11 Unfortunately the F, hybrids were sterile inter se, so that, for later generations, Detlefsen was restricted to continued back-crosses between F, animals and guinea-pigs. 12 NoTe. At the time of preparing this paper, I was not acquainted with Castle's later results on size-inheritance in rabbit crosses, CarnegieInstitution, Pubi., No. 320, 1922.