ve
been turned mainly in one direction for long together; and hence the
consequent modifications will also be mainly in fixed and definite
directions for many successive generations; as in the direction of a
warmer or cooler covering; of a better means of defence or of attack in
relation to such and such another species; of a longer neck and longer
legs, or of whatever other modification the gradually changing
circumstances may be rendering expedient. It is easy to understand the
accumulation of slight successive modifications which thus make their
appearance in given organs and in a set direction.

With Mr. Darwin, on the contrary, the variations being accidental, and
due to no special and uniform cause, will not appear for any length of
time in any given direction, nor in any given organ, but will be just as
liable to appear in one organ as in another, and may be in one
generation in one direction, and in another in another.

In confirmation of the above, and in illustration of the important
consequences that will follow according as we adopt the old or the more
recent theory, I would quote the following from Mr. Mivart's 'Genesis of
Species.'

Shortly before maintaining that two similar structures have often been
developed independently of one another, Mr. Mivart points out that if we
are dependent upon indefinite variations only, as provided for us by Mr.
Darwin, this would be "so improbable as to be practically
impossible."[344] The number of possible variations being indefinitely
great, "it is therefore an indefinitely great number to one against a
similar series of variations occurring and being similarly preserved in
any two independent instances." It will be felt (as Mr. Mivart presently
insists) that this objection does not apply to a system which maintains
that in case an animal feels any given want it will gradually develop
the structure which shall meet the want--that is to say, if the want be
not so great and so sudden as to extinguish the creature to which it has
become a necessity. For if there be such a power of self-adaptation as
thus supposed, two or more very widely different animals feeling the
same kind of want might easily adopt similar means to gratify it, and
hence develop eventually a substantially similar structure; just as two
men, without any kind of concert, have often hit upon like means of
compassing the same ends. Mr. Spencer's theory--so Mr. Mivart tells
us--and certainly that of Lam