he black and the white rabbit, only two
factors are concerned, and one of them is brought in from each of the {60}
two parents. But in other cases the nature of the reversion may be more
complicated owing to a larger number of factors being concerned, though the
general principle remains the same. Careful breeding from the reversions
will enable us in each case to determine the number and nature of the
factors concerned, and in illustration of this we may take another example
from rabbits. The Himalayan rabbit is a well-known breed. In appearance it
is a white rabbit with pink eyes, but the ears, paws, and nose are black
(Pl. I., 2). The Dutch rabbit is another well-known breed. Generally
speaking, the anterior portion of the body is white, and the posterior part
coloured. Anteriorly, however, the eyes are surrounded by coloured patches
extending up to the ears, which are entirely coloured. At the same time the
hind paws are white (cf. Pl. I., 1). Dutch rabbits exist in many varieties
of colour, though in each one of these the distribution of colour and white
shows the same relations. In the experiments about to be described a yellow
Dutch rabbit was crossed with a Himalaya. The result was a reversion to the
wild agouti colour (Pl. I., 3). Some of the F_1 individuals showed white
patches, while others were self-coloured. On breeding from the F_1 animals
a series of coloured forms resulted in F_2. These were agoutis, blacks,
yellows, and sooty yellows, the so-called tortoise shells of the fancy (Pl.
I., 4-7).

[Illustration: PLATE I.

1, Yellow Dutch Rabbit; 2, Himalayan; 3, Agouti ( = grey) F_1 reversion;
4-8, F_2 types, viz.: 4, Agouti; 5, Yellow; 6, Black; 7, Tortoiseshell; 8,
Himalayan.]

{61}

Yellow x Himalayan
|
+-------------+
Agouti x Agouti
|
+--------+------+-------+----------+
Agouti Yellow Black Tortoise Himalayan
Shell
(27) (9) (9) (3) (16)

In addition to these appeared Himalayans with either black points or with
lighter brownish ones, and the proportions in which they came showed the
Himalayan character to be a simple recessive. A certain number of the
coloured forms exhibited the Dutch marking to a greater or less extent, but
as its inheritance in this set of experiments is complicated and has not
yet been worked out, we may for the present neglect it and con