seemingly just as deserving of the rank of distinct species as many now
listed in scientific books, it only shows that our lists are sadly at
fault, and that they are not all species that are called species. These
experiments merely indicate that _the parent form possesses more
potential characters than it can give expression to in a single
individual form_, some of them being necessarily latent or hidden, and
that when these latent ones show themselves they must do so at the
expense of others which become latent or hidden in their turn. This
_vital elasticity_, as it may be termed, or the vital rebound under
definite conditions, is indeed a prime characteristic of the species
just as it is of the individual; but like that of the individual the
vital elasticity of the species is strictly bounded by comparatively
narrow limits beyond which we have never seen a single type pass under
either natural or artificial conditions. Mutations can be made according
to Mendel's Law; but when we have made them once _we can always be sure
of producing the_ _very same mutants again in the very same way_, as
surely as we produce a definite chemical compound; and when we have made
it _we can always resolve it at will back into its original form_, just
as we can a chemical compound. And so, where is the evolution? or how do
these facts throw any light on the problem of the origin of species, any
more than chemical compounds throw light on the origin of the elements?
Obviously in biology as in chemistry we are only working in a circle,
merely marking time.

And the bearing of these facts on the other problem of the transmission
of acquired characters is quite obvious. Mendelism provides no place for
any such transmission. Mendel's Law is sometimes called the law of
_alternative inheritance_, thus embodying in its name the thought that
offspring may show the characters possessed by one parent or by the
other, but that it cannot develop any characters whatever which were not