HOUWINK’S EXPER. CONC. THE ORIGIN OF SOME DOMESTIC ANIMALS 249 
The F, blackred hen 276.9 gave, with the blackred cock 276.1, the F3 
generation 607 consisting of the following birds: 
607.1 sex unknown born June 5th 1921 dispappeared July 21 1921 
607.2 4 born June 5th 1921 sent to Mook Dec. 1921 still alive Dec. 1923 
607.3 & born June 5th 1921 sent to Mook Dec. 1921 stuffed Feb.13 1922 
607.4 4 born June 5th 1921 sent to Mook Dec. 1921 stuffed Febr. 13 1922 
Of these 3 cocks two are yellow Duckwings, to wit 607.2 (still living 
Pl. IX fig. 8) and 607.4, while 607.3 is blackred e. g. contains the gold- 
factor. 
Either one of the blackred parents consequently must have posses- 
sed the silverfactor S and also the inhibiting factor I which prevented 
it to manifest itself. 
Before we proceed to discuss this point, we must remind the reader 
of the way in which the silver and gold factors behave in crossing. 
The hen in poultry is heterozygous, as to sex, so that it forms two 
kinds of eggs M eggs (male ones) and F eggs (female ones). The gold fac- 
tor, to be indicated by s, (absence of S) enters as willingly into the M 
as into the F eggs, but the silverfactor S refuses to enter into the 
F eggs and consequently only occurs in the M eggs of a silver 
hen. 
The cock, on the other hand, forms but one kind of gametes, M, half 
of which, in a heterozygous silvercock, contain the factor S while the 
other half does not. 
We consequently see that a silver hen is always Ss, a silvercock may 
be either Ss or SS, and both a gold hen and a gold cock are always 
SS. 
The following cases are therefore possible : 
