y--has led
to the attempt to gratify them; that the actions thus induced, having
become habitual and energetic, have occasioned the development of organs
adapted for their performance; that the force which excites organic
movements can in the case of the lowest animals exist outside them and
yet animate them; that this force was subsequently introduced into the
animals themselves, and fixed within them; and, lastly, that it gave
rise to sensibility and, in the end, to intelligence."[208] The reader
had better be on his guard here, and whenever Lamarck is speculating
about the lowest forms of action and sensation. I have thought it well,
however, to give enough of these speculations, as occasion arises, to
show their tendency.

"Sensation is not the proximate cause of organic movements. It may be so
with the higher animals, but it cannot be shown to be so with plants,
nor even with all known animals. At the outset of life there was none of
that sensation which could only arise where organic beings had already
attained a considerable development. Nature has done all by slow
gradations, both organs and faculties being the outcome of a progressive
development.[209]

"The mere composition of an animal is but a small part of what deserves
study in connection with the animal itself. The effects of its
surroundings in causing new wants, the effects of its wants in giving
rise to actions, those of its actions in developing habits and
tendencies, the effects of use and disuse as affecting any organ, the
means which nature takes to preserve and make perfect what has been
already acquired--these are all matters of the highest importance.[210]

"In their bearing upon these questions the invertebrate animals are more
important and interesting than the vertebrate, for they are more in
number, and being more in number are more varied; their variations are
more marked, and the steps by which they have advanced in complexity are
more easily observed.[211]

"I propose, therefore, to divide this work into three parts, of which
the first shall deal with the conventions necessary for the treatment of
the subject, the importance of analogical structures, and the meaning
which should be attached to the word species. I will point out on the
one hand the evidence of a graduated descending scale, as existing
between the highest and the lowest organisms; and, on the other, the
effect of surroundings and habits on the organs of living beings, a