276 E. J. ALLEN AND E. W. SEXTON. 
Following Bateson and Punnett we may assume a colour factor C, 
which with its absence ¢ forms an allelomorphic pair. In the absence 
of C the factors for black and red in the retinal pigment do not produce 
any visible effect. The constitution of the pure red male would then 
be : and of the albino female gee where B and R are the factors for 
black and red respectively. 
The mating of these should give in F, :— 
Cc BR, a black carrying the factor for “red” and also the factor 
POrealbino. 3% 
CcRR, a pure red carrying the factor for “ albino.” 
FA. Generation. Black « Black. 
The three black-eyed young of this F, generation were 2 females and 
1 male (PI. I: I.A.B.C.). The male was mated with the females in turn 
and three broods were obtained from each. The total number of young 
was 119, of which 61 were black-eyed, 28 red-eyed, and 30 albino-eyed. 
Theoretically the cross 
Cre Bune << © cebu 
gives gametes CB 
which with chance meetings would give zygotes :— 
CB CB CB CB 
CB CR CoBe dees 
CHIR Tati Old 8s CR CR 
CB CR GuB al Gk 
ec B Cobre acy ase 
CB CUR Salcombe dene 
eR Gut Ca ec R 
CB CReaikacsB | ¢ R 
That is out of every 16 young there are 9 Black-eyed, viz. :— 
1 with constitution C C BB 
Dees ie Gie-B-B 
De a CC BR 
anes se Cie BR 
* We shall for convenience refer to the factor ¢, which on the hypothesis represents 
the absence of the colour factor C, as the ‘ albino factor.” 
