four laws of evolution in the first volume of his Invertebrate
(1) Life tends to increase the volume & dimensions of
organisms, within limits.
(2) Production of new organs arises from persistent need, one translation of the French besoin, rather than want.
The latter implies a teleological, the former an immediate motivation.
(3) Development of organs are proportional to use & disuse.
(4) Acquired or modified characteristics are preserved as hereditary elements that are transmitted to the next generation.
Lamarck does not propose a mechanism.