262 Edmund B. Wilson: 
Some of the diffieulties of the first alternative are as follows. 
In insects where the female is homogametic, and which follow 
the formulas: 
a) Egg X + Spermatozoon X = XX (Female) \ a] 
b) Egg X + Spermatozoon noX = X (Male) |} 1 A 
that if the sex-chromosomes be specifically male and female deter- 
minants, the X-chromosome of the male must be a male-deter- 
minant (X 9). It is equally clear from Formula b that in fertili- 
zation this chromosome is derived from the egg, not from the sperm. 
Upon the introduction of this chromosome into the egg, 
however, the product is a female (Formula a). We must therefore 
assume that in this case the X-chromosome of the egg is a dominant 
female-determinant (X 2). Thefemale formula thus becomes X 2 (X 3) 
and the male X 2. Under this view the Y-chromosome (if present) 
was assumed to represent a recessive female determinant (both 
sexes being heterozygous for sex); and its frequent reduction or final 
disappearance were ascribed to its invariably recessive character. 
Of the many diffieulties which this interpretation involves, 
I will indicate three principal ones. 
1. The X 2 spermatozoa must fertilize only the X 2 eggs 
and vice versa; for the condition X X does not exist. Such 
”selective fertilization‘‘ has always seemed to me improbable. 
3. The female is thus rendered heterozygous like the male; 
but in case of the Diptera — a group which shows the same 
cytological relations (Stevens, 1908, 1910a) as the Hemiptera 
or the Coleoptera — Morgan’s experiments on Drosophila (1910) 
prove the female to be in fact homozygous. 
3. In the bee, all unfertilized eggs (reduction having taken 
place) produce males, fertilized eggs females. All the mature 
eggs must therefore bear the male character (X 3), and the female 
character (X ?) must be introduced by the spermatozoon — & 
double contradietion. We might assume with Beard that there 
are two kinds of eggs, of which only one (the X ? class) are 
capable of fertilization; but of this there is no evidence, and such 
an assumption seems to be excluded by the observations of 
Maupas and Whitney on rotifers (in which the sexual relations 
are the same as in the bee). 
In view of these and other difheulties I long since became 
convinced that some form of the second or quantitative inter- 
