508 A. H. STURTEVANT 
The only conclusions which I feel safe in drawing from these 
data are that the White Wyandotte is a recessive white, lacking 
a color producer, and that it carries a silver laced determiner. 
Bateson (’02) gives confirmatory evidence for the first of these 
conclusions. 
SEX FORMULAE 
It will be noted that I have used above the MM, Mm scheme 
for sex formulae in preference to the more usual Ff, ff formula 
(see Morgan, 711). I have made the change because the formula 
used here gives a mechanism which allows both complete sex- 
linkage, and also incomplete association with the sex-determiner. 
I shall now present the evidence which has led to this view. 
It seems to me that the evidence now before us warrants the 
conception of the chromosomes as the carriers of Mendelian 
factors or genes, as a working hypothesis. This conception is 
especially helpful in considerations of sex-linkage and the other 
forms of gametic coupling or associative inheritance. The recent 
hypothesis put forward by Morgan (’11 a, ’11 b, ’11 c) to explain 
these phenomena seems to me to overcome the old difficulties 
encountered by the chromosome hypothesis of Mendelian inher- 
itance. I shall make this conception the basis of my argument 
in favor of the MM, Mm scheme. 
Sex-linked inheritance of the type concerned here has now 
been known for some time, and has been recognized in Lepi- 
doptera and in birds, as follows: Abraxas (Doncaster and Raynor, 
06; Doncaster, ’08), canaries (Durham and Marryatt, ’08), fowls 
(Bateson, ’09; Spillman, 709; Goodale, ’09, 710; Pearl and Sur- 
face, 710; Bateson and Punnett, 711; Davenport, ’11; Sturtevant, 
11), and ducks (Goodale, ’11). 
Since my argument for the MM, Mm sex formula depends 
largely upon certain cases which I believe to represent partial 
sex-linkage, it will perhaps be well to present in some detail the 
evidence for the existence of this phenomenon. In this category 
I have included three cases of the Abraxas type (one in the fowl, 
one in the canary, and one in Aglia tau), and one, which I shall 
describe later, in the Drosophila type of sex-linkage. 
