self; but they have been very carefully studied. Now, the
curious thing is this, that although you have the same elements in
the experiment in each case, the offspring is entirely different in
character, according as the male influence comes from the Ass or the
Horse. Where the Ass is the male, as in the case of the Mule, you find
that the head is like that of the Ass, that the ears are long, the
tail is tufted at the end, the feet are small, and the voice is an
unmistakable bray; these are all points of similarity to the Ass; but,
on the other hand, the barrel of the body and the cut of the neck are
much more like those of the Mare. Then, if you look at the Hinny,--the
result of the union of the Stallion and the she-Ass, then you find it is
the Horse that has the predominance; that the head is more like that
of the Horse, the ears are shorter, the legs coarser, and the type is
altogether altered; while the voice, instead of being a bray, is the
ordinary neigh of the Horse. Here, you see, is a most curious thing: you
take exactly the same elements, Ass and Horse, but you combine the sexes
in a different manner, and the result is modified accordingly. You
have in this case, however, a result which is not general and
universal--there is usually an important preponderance, but not always
on the same side.

Here, then, is one intelligible, and, perhaps, necessary cause of
variation: the fact, that there are two sexes sharing in the production
of the offspring, and that the share taken by each is different and
variable, not only for each combination, but also for different members
of the same family.

Secondly, there is a variation, to a certain extent--though, in
all probability, the influence of this cause has been very much
exaggerated--but there is no doubt that variation is produced, to a
certain extent, by what are commonly known as external conditions,--such
as temperature, food, warmth, and moisture. In the long run, every
variation depends, in some sense, upon external conditions, seeing that
everything has a cause of its own. I use the term "external conditions"
now in the sense in which it is ordinarily employed: certain it is, that
external conditions have a definite effect. You may take a plant which
has single flowers, and by dealing with the soil, and nourishment, and
so on, you may by-and-by convert single flowers into double flowers,
and make thorns shoot out into branches. You may thicken or make various