84 Experimental Zoology 
different according to the kind of albinos that he used. For 
example, albinos that had been derived through a gray ancestor, 
z.e. the so-called extracted albinos, when bred with the black 
strain produced gray offspring. If, however, albinos that had 
been derived through a previous cross with a black mouse were 
bred with a black, the offspring were black. Again, albinos 
derived from a previous cross with a yellow gave either mixed 
yellow and gray, or mixed yellow and black. These results 
show that although albinos may all appear alike and breed per- 
fectly true with each other, they belong in reality to different 
classes, whose latent characters are dependent on previous 
influences. Results of this sort are difficult to account for on 
the supposition that the germ-cells are pure. This property of 
latency is not something peculiar to albinos as certain published 
statements might have lead one to infer, but holds for the differ- 
ent colors also. A black race that breeds true may carry 
another latent color that can be brought out by crossing. Un- 
less this fact is also taken into account the crosses with albinos 
may be misinterpreted. | 
Experiments with waltzing mice have been made by Haacke, 
von Guaita, and Darbishire. These mice are black, or 
white, or yellow and white; the mixed colors introducing 
a complication into the results, so far as color inheritance 
is concerned. As has been said, von Guaita’s results with 
these mice were not considered from the point of view 
of Mendel’s law, but Bateson, who has later analyzed the data, 
finds in some cases what seems to be an approximation to 
the expected proportions; in other cases this is not evident. 
A few of von Guaita’s facts and their possible interpreta- 
tions may be given. When the black-and-white waltzers were 
bred to ordinary albinos, the first offspring (F',) were gray, like 
the house mouse, and of the same size, which is larger than 
that of the waltzing race. They also show the wild disposition. 
These mice (F) when inbred produced albinos and four colored 
types,—black, gray, black-and-white, and gray-and-white. 
There were 14 albinos and 30 colored individuals. The relation 
