higher
orders of plants and animals were thus supposed to be comparatively
modern, and to have been derived in a long series of generations from
those of more simple conformation, some farther hypothesis became
indispensable, in order to explain why, after an indefinite lapse of
ages, there were still so many beings of the simplest structure. Why
have the majority of existing creatures remained stationary throughout
this long succession of epochs, while others have made such prodigious
advances? Why are there such multitudes of infusoria and polyps, or of
confervae and other cryptogamic plants? Why, moreover, has the process of
development acted with such unequal and irregular force on those classes
of beings which have been greatly perfected, so that there are wide
chasms in the series; gaps so enormous, that Lamarck fairly admits we
can never expect to fill them up by future discoveries?

The following hypothesis was provided to meet these objections. Nature,
we are told, is not an intelligence, nor the Deity; but a delegated
power--a mere instrument--a piece of mechanism acting by necessity--an
order of things constituted by the Supreme Being, and subject to laws
which are the expressions of his will. This Nature is _obliged_ to
proceed gradually in all her operations; she cannot produce animals and
plants of all classes at once, but must always begin by the formation of
the most simple kinds, and out of them elaborate the more compound,
adding to them, successively, different systems of organs, and
multiplying more and more their number and energy.

This nature is daily engaged in the formation of the elementary
rudiments of animal and vegetable existence, which correspond to what
the ancients termed _spontaneous generation_. She is always beginning
anew, day by day, the work of creation, by forming monads, or "rough
draughts" (abauches), which are the only living things she gives birth
to _directly_.

There are distinct primary rudiments of plants and animals, and
_probably_ of each of the great divisions of the animal and vegetable
kingdoms.[797] These are gradually developed into the higher and more
perfect classes by the slow but unceasing agency of two influential
principles: first, _the tendency to progressive advancement_ in
organization, accompanied by greater dignity in instinct, intelligence,
&c.; secondly, _the force of external circumstances_, or of variations
in the physical condition of the earth, o