These, with many articles by other men of science, illustrated by
plates, indicate that during the years of social unrest and upheaval in
Paris, and though France was also engaged in foreign wars, the
philosophers preserved in some degree, at least, the traditional calm of
their profession, and passed their days and nights in absorption in
matters biological and physical. In 1801 appeared his _Systeme des
Animaux sans Vertebres_, preceded by the opening discourse of his
lectures on the lower animals, in which his views on the origin of
species were first propounded. During the years 1793-1798, or for a
period of six years, he published nothing on zooelogy, and during this
time only one paper appeared, in 1798, on the influence of the moon on
the earth's atmosphere. But as his memoirs on fire and on sound were
published in 1798, it is evident that his leisure hours during this
period, when not engaged in museum work and the preparation of his
lectures, were devoted to meditations on physical and meteorological
subjects, and most probably it was towards the end of this period that
he brooded over and conceived his views on organic evolution.

It appears that he was led, in the first place, to conchological studies
through his warm friendship for a fellow naturalist, and this is one of
many proofs of his affectionate, generous nature. The touching story is
told by Etienne Geoffroy St. Hilaire.[36]

"It was impossible to assign him a professorship of botany. M. de
Lamarck, then forty-nine years old, accepted this change in his
scientific studies to take charge of that which everybody had
neglected; because it was, indeed, a heavy load, this branch of
natural history, where, with so varied relations, everything was to
be created. On one group he was a little prepared, but it was by
accident; a self-sacrifice to friendship was the cause. For it was
both to please his friend Bruguiere as well as to penetrate more
deeply into the affections of this very reserved naturalist, and
also to converse with him in the only language which he wished to
hear, which was restricted to conversations on shells, that M. de
Lamarck had made some conchological studies. Oh, how, in 1793, did
he regret that his friend had gone to Persia! He had wished, he had
planned, that he should take the professorship which it was proposed
to create. He would at least supply his place; it was in answer to
the yearnings of his s