being." A scientific definition, of which an unwarrantable hypothesis
forms an essential part, carries its condemnation within itself; but,
even supposing such a definition were, in form, tenable, the
physiologist who should attempt to apply it in Nature would soon find
himself involved in great, if not inextricable, difficulties. As we
have said, it is indubitable that offspring 'tend' to resemble the
parental organism, but it is equally true that the similarity attained
never amounts to identity, either in form or in structure. There is
always a certain amount of deviation, not only from the precise
characters of a single parent, but when, as in most animals and many
plants, the sexes are lodged in distinct individuals, from an exact mean
between the two parents. And indeed, on general principles, this
slight deviation seems as intelligible as the general similarity, if we
reflect how complex the co-operating "bundles of forces" are, and how
improbable it is that, in any case, their true resultant shall coincide
with any mean between the more obvious characters of the two parents.
Whatever be its cause, however, the co-existence of this tendency to
minor variation with the tendency to general similarity, is of vast
importance in its bearing on the question of the origin of species.

As a general rule, the extent to which an offspring differs from its
parent is slight enough; but, occasionally, the amount of difference is
much more strongly marked, and then the divergent offspring receives
the name of a Variety. Multitudes, of what there is every reason to
believe are such varieties, are known, but the origin of very few has
been accurately recorded, and of these we will select two as more
especially illustrative of the main features of variation. The first
of them is that of the "Ancon," or "Otter" sheep, of which a careful
account is given by Colonel David Humphreys, F.R.S., in a letter to Sir
Joseph Banks, published in the Philosophical Transactions for 1813. It