HOUWINK’S EXPER. CONC. THE ORIGIN OF SOME DOMESTIC ANIMALS 247 
explanation. It may of course hold good, on the assumption that pairs 
of two chromosomes or more are responsible for the waxy tips of sonne- 
ati, as the number of F, animals and of those of later generations is so 
small, that recombinations of those chromosomes could hardly be ex- 
pected to occur among so small a progeny; in the same way of course 
the absence of anything even approaching the Sonnerat type of hen in 
F, or later generations, may be explained, but we are inclined to believe 
that there must be something else at the bottom of it. (see , Conclusi- 
ons’ at the end of this article) 
The most important fact which came to light is the appearance of the 
duckwing pattern in F,, because this pattern is due to a dominating silver- 
factor which can not have been present in our bankantams which are black- 
red. 
Of this Punnett says in his Heredity in poultry p. 66: 
„Again, the difference between the Duckwing and the Blackred type 
is one involving the presence or absence of the silver factor. The addi- 
tion of the factor S to a blackred turns it into a Duckwing. 
From this appearance of the Duckwing pattern in the F, of the Sonnerat 
cross, it therefore follows that the silverfactor has been introduced into our 
domestic poultry by crossing bankiva, in all probability, with Sonneratt, 
and that this has afterwards, by repeated crossing, given rise to the different 
silver-varieties of so many of our present races of domestic poultry. 
Mr. Houwink is to be congratulated on this important result of his 
work as to the origin of our domestic poultry. There remains to be ex- 
plained why the F, birds of the cross bankantam (blackred) x Sonne- 
rati were no Duckwings as the silverfactor was introduced into the cross 
by sonnerati. 
An inspection of a sonnerati, shows at once, that although the sil- 
ver-factor must, judging by Mr. Houwinx’s result, be present in it, 
it does not manifest itself, as neither a Sonnerat-cock nor a Sonnerat- 
hen can be described as , silver”. 
Sonnerat must therefore contain a factor which prevents the Silver 
factor S to manifest itself, let us call this inhibiting factor I and assume 
that Sonnerat’s are homozygous for both of these factors, so that Son- 
nerat’s are Soll. 
Blackreds must than be assumed to be ssii, and the F, hybrids will 
consequently be Ssli, and, on account of the presence of I be unable to 
manifest the silverfactor which they contain; perhaps it is owing to the 
