o explain the causes of a metamorphosis in animals, one
is compelled to go back to the primary factors of organic
evolution, such as the change of environment, whether the factors be
cosmical (gravity), physical changes in temperature, effects of
increased or diminished light and shade, under- or over-nutrition,
and the changes resulting from the presence or absence of enemies,
or from isolation. The action of these factors, whether direct or
indirect, is obvious, when we try to explain the origin or causes of
the more marked metamorphoses of animals. Then come in the other
Lamarckian factors of use and disuse, new needs resulting in new
modes of life, habits, or functions, which bring about the
origination, development, and perfection of new organs, as in new
species and genera, etc., or which in metamorphic forms may result
in a greater increase in the number of, and an exaggeration of the
features characterizing the stages of larval life.

"VI. _The Adequacy of Neolamarckism_.

"It is not to be denied that in many instances all through the
ceaseless operation of these fundamental factors there is going on a
process of sifting or of selection of forms best adapted to their
surroundings, and best fitted to survive, but this factor, though
important, is quite subordinate to the initial causes of variation,
and of metamorphic changes.

"Neolamarckism,[226] as we understand this doctrine, has for its
foundation a combination of the factors suggested by the Buffon and
Geoffroy St. Hilaire school, which insisted on the direct action of
the _milieu_, and of Lamarck, who relied both on the direct (plants
and lowest animals) and on the indirect action of the environment,
adding the important factors of need and of change of habits
resulting either in the atrophy or in the development of organs by
disuse or use, with the addition of the hereditary transmission of
characters acquired in the lifetime of the individual.

"Lamarck's views, owing to the early date of his work, which was
published in 1809, before the foundation of the sciences of
embryology, cytology, palaeontology, zooegeography, and in short all
that distinguishes modern biology, were necessarily somewhat crude,
though the fundamental factors he suggested are those still invoked
by all thinkers of Lamarckian tendencies.

"Neolamarckism gathers up and makes use of the factors both of th