758 Isabel McCracken 
ing mothers; Broods E, F, G and H each furnished four bivoltin- 
and six univoltin-producing mothers; Brood I furnished eight ~ 
bivoltin and two univoltin-producing mothers and Brood J fur- 
nished ten bivoltin- and no univoltin-producing mothers. 
Thus it is that the averages of the various series as wholes do 
not represent the actual brood condition of each brood within the 
series. Certain broods are totally prepotent in the direction of 
the expression of univoltinism, certain broods are totally pre- 
potent in the direction of the expression of bivoltinism. ‘The 
whole study indeed points to an underlying “law of potency.” 
Such a law has been suggested by Davenport,’ but as yet the study 
of heredity is too young for any adequate expression of the law 
or any comprehension of its real significance. 
Two years after this study was begun K. Toyama published a 
paper on “Some Silkworm crosses with special reference to Men- 
del’s Law of Heredity.” The main part of his paperis devoted 
to a consideration of crosses involving larval and cocoon charac- 
ters.- However, he devotes one page to a consideration of a 
cross similar to that of the present study. In Toyama’s report, 
of five univoltin + bivoltin crosses, the eggs laid by the moth 
were, in four cases, like the maternal race,—that is, bivoltin when 
the mother was bivoltin (2 cases) and univoltin when the mother 
was univoltin (2 cases). In one cross, the eggs followed the pater- 
nal race character. Toyama adds a footnote reference to the 
effect that “further experiments show that the first cross is always 
maternal in crossing with pure breeds.’ It will be remembered 
that in the original cross of the present work (1904), the first 
generation followed the character of the maternal race, as in 
Toyama’s four crosses; namely, was univoltin from a univoltin 
female and a bivoltin male. 
In the spring of 1908, after it was determined that certain 
broods reared from 1997 parents were furnishing bivoltin-produc- 
ing mothers only, and others univoltin-producing mothers only, 
when mated with males similarly reared (whether or not from 
identical broods), it was determined to test these strains with 
3 Davenport: Heredity and Mendel’s Law. Proc. of the Wash. Acad. of Sciences, ix, 1907, p. 184. 
4 Bulletin of the College of Agriculture, Tokyo Imperial Univ., vol. vii, 259-293. 
