Experimental Hybridizing                    83

white background; spotted or pied or piebald mice are those
in which these various colors appear in splotches or marks.
In addition to these kinds, a white mouse with dark eyes is
known, which is probably — to judge from other white animals
with black eyes — not derived from an albino, but from a
spotted animal in which the spots of dark pigment have disap¬
peared except in the eyes. The so-called dancing mice that
whirl around at times are said to be of Japanese origin, and may
have originated from a different wild variety.

Experiments on mice have been carried out by a number of
investigators, the principal results being those of von Guaita,
Cuenot, Parsons, Darbishire, Castle, Allen, Davenport, Schuster,
Haacke, and others. Von Guaita's results were not consid¬
ered by him in the light of the Mendelian ratio, but Bateson and
Davenport have more recently examined them and have pointed
out that many of them appear to follow Mendel's law.

Cuenot's results conform closely to the Mendelian law. He
found that when a gray mouse is paired with an albino, the off¬
spring in the first generation {F^ are always gray mice — the
gray dominating over albinism. The next generation {F^ from
the inbred dominant gray mice gave 198 gray and 72 albino
mice, i.e. in the ratio of 2.75 : i, a near approach to the expecta¬
tion of 3 :1. Later Cuenot reported that his "pure" gray ^ mice
of the third filial generation {F^ when crossed yith albinos gave
several black mice. These black mice when bred with certain
albinos gave black mice, which appeared to be B(W), i.e. black
dominant, white recessive, for, when bred inter se, the offspring
were three blacks to one albino. Some of these blacks were
shown to be "pure" and produced a race of pure blacks. When
individuals of this black strain were bred to ordinary gray mice,
the black was recessive, giving in the second generation three
grays to one black.

Cuenot made a further discovery of great interest. He found
when he bred the black mice to albinos that the results were

■■^ These were the offspring of the second generation that had bred true and
shown themselves to be pure G's.