actions which have become
habitual--there will from this result the use of such a part by
preference to that of another, and in certain cases the total lack
of use of any part which has become useless.

"Nothing of all this should be considered as a hypothesis or as a
mere peculiar opinion; they are, on the contrary, truths which
require, in order to be made evident, only attention to and the
observation of facts.

"We shall see presently by the citation of known facts which prove
it, on one side that the new wants, having rendered such a part
necessary, have really by the result of efforts given origin to this
part, and that as the result of its sustained use it has gradually
strengthened it, developed, and has ended in considerably increasing
its size; on the other side we shall see that, in certain cases, the
new circumstances and new wants having rendered such a part wholly
useless, the total lack of use of this part has led to the result
that it has gradually ceased to receive the development which the
other parts of the animal obtain; that it gradually becomes
emaciated and thin; and that finally, when this lack of use has been
total during a long time, the part in question ends in disappearing.
All this is a positive fact; I propose to give the most convincing
proofs.

"In the plants, where there are no movements, and, consequently, no
habits properly so called, great changes in circumstances do not
bring about less great differences in the development of their
parts; so that these differences originate and develop certain of
them, while they reduce and cause several others to disappear. But
here everything operates by the changes occurring in the nutrition
of the plant, in its absorptions and transpirations, in the amount
of heat, light, air, and humidity which it habitually receives;
finally, in the superiority that certain of the different vital
movements may assume over others.

"Between individuals of the same species, some of which are
constantly well nourished, and in circumstances favorable to their
entire development, while the others live under reversed
circumstances, there is brought about a difference in the condition
of these individuals which gradually becomes very remarkable. How
many examples could I not cite regarding animals and plants, which
would confirm the grounds for this view! Now, if the circumstances
rem