1907.| Transmission of certain Coat Characters in Rats. 115 
and 44 it had none but “ Irish” ’ members in its offspring, 16 in number, 
because the albino with which it was mated had come probably from a 
piebald ancestry, and was carrying nothing but piebald pattern and black 
determiners. But in experiment 45 it was mated with an albino in which 
it was probable that the grey determiner was present, because of its extrac- 
tion from a grey parent. And grey individuals then appeared in its progeny. 
Grey individuals also appeared in the offspring of a sister albino when it was 
mated with a homozygote self-black. 
(7) Summary of Results. 
The figures within brackets indicate the page where the matter of the 
summary may be found. 
1. That black is dominant to albinism (113). The dominance is not 
complete, some ventral white being always present. In relation to 
dominance this is perhaps not of particular significance, since ventral white 
patches are known to occur in both grey and black wild rats. This conclusion 
is confirmatory of that deduced from Crampe’s results, and arrived at in 
Doncaster’s experiments. 
It is theoretically conceivable that the incompleteness of the dominance is 
due to the influence of the factor s (= absence of self-pattern) brought in by 
the albino. 
2. Expected types do not all always appear in any one litter of young, and 
frequently not until the third litter (106). 
Doneaster has also shown that there is considerable diversity in the 
proportions of the indivduals of each type in successive litters, but the 
examples published by him do not show whether a type present in one litter 
may be absent in another, as in several of my experiments. 
3. Predictions based upon the doctrine of gametic purity and of dominance 
have not in these experiments (including those not yet published) been 
falsified by the appearance of unpredicted types. With but few exceptions, 
the predictions with respect to the kind of types expected are fulfilled, and 
approximately so with respect to proportions. The exceptions are due to 
the smallness of the number of offspring in certain cases. 
4. The conception (hitherto a matter of deduction) that albinoes are the 
bearers of hidden factors, has been ocularly demonstrated for the piebald, 
“Trish” and self patterns (111). In peas a somewhat analogous phenomenon 
has been seen by Lock. 
5. That completely self-black extracted torms are homozygous for black 
(110, 113). 
This conclusion appears not to harmonise with some of Doncaster’s 
