ore in this direction.

From Treviranus came, in 1802, his work on biology, and in this he gave
forth the idea that from forms of life originally simple had arisen all
higher organizations by gradual development; that every living feature
has a capacity for receiving modifications of its structure from
external influences; and that no species had become really extinct, but
that each had passed into some other species. From Lamarck came
about the same time his Researches, and a little later his Zoological
Philosophy, which introduced a new factor into the process of
evolution--the action of the animal itself in its efforts toward a
development to suit new needs--and he gave as his principal conclusions
the following:

1. Life tends to increase the volume of each living body and of all its
parts up to a limit determined by its own necessities.

2. New wants in animals give rise to new organs.

3. The development of these organs is in proportion to their employment.

4. New developments may be transmitted to offspring.

His well-known examples to illustrate these views, such as that of
successive generations of giraffes lengthening their necks by stretching
them to gather high-growing foliage, and of successive generations of
kangaroos lengthening and strengthening their hind legs by the necessity
of keeping themselves erect while jumping, provoked laughter, but
the very comicality of these illustrations aided to fasten his main
conclusion in men's memories.

In both these statements, imperfect as they were, great truths were
embodied--truths which were sure to grow.

Lamarck's declaration, especially, that the development of organs is in
ratio to their employment, and his indications of the reproduction
in progeny of what is gained or lost in parents by the influence of
circumstances, entered as a most effective force into the development of
the evolution theory.

The next great successor in the apostolate of this idea of the universe
was Geoffroy Saint-Hilaire. As early as 1795 he had begun to form a
theory that species are various modifications of the same type, and this
theory he developed, testing it at various stages as Nature was more
and more displayed to him. It fell to his lot to bear the brunt in a
struggle against heavy odds which lasted many years.

For the man who now took up the warfare, avowedly for science
but unconsciously for theology, was the foremost naturalist then
living--Cuvier. His scie