Jean Baptiste Pierre Antoine De Monet De Lamarck, a French naturalist, born at Barentin, Picardy, Aug. 1, 1744, died in Paris, Dec. 18, 1829. He was a younger son of a noble family, formerly of Bearn, and being destined for the church was sent to the Jesuits' college at Amiens; but his father dying when he was 17 years old, he left his studies and joined the army under the duke de Broglie. He served until the close of the seven years' war, when he became incapacitated for military duty by an accident, returned to Paris, and studied medicine and the physical sciences. In 1776 he began his career as an author by the publication of his Memoire sur les vapeurs de l'at-mospliere. In 1778 he published his Flore francaise, containing a new arrangement of plants which was commended by Buffon and the academy of sciences. About the same time he accompanied the younger Buffon on a tour through Germany and Holland to procure botanical specimens; and he became also a companion in the botanical excursions of J. J. Rousseau. Being appointed editor of the botanical department of Panckoucke's Encyclopedic methodique, the results of his researches were embodied in that work. The outbreak of the French revolution interrupted it and terminated Lamarck's botanical labors.
In 1793, although he had given comparatively little attention to zoology, he was intrusted with the department of invertebrata in the museum of natural history in Paris. This branch of natural history became thenceforth the absorbing study of his life, and his lectures upon it, begun in 1794, were continued until the failure of his eyesight in 1818 incapacitated him for the duty. His first important work on this subject, Systeme des animaux sans vertebres (1801), was the forerunner of a more elaborate treatise published many years later. In 1809 appeared his Philosophie zoo-logique (2 vols. 8vo), in which his theory of the development of animal functions, previously hinted at in an early work, is set forth at considerable length. It was his opinion that new organs could be produced in animals by the simple exertion of the will, called into action by the creation of new wants; and that the organs thus acquired could be transmitted by generation. In support of this doctrine, which is called appetency, he cited the existence of tentacula on the head of the snail, which derive their origin from the desire of the animal, united with endeavor perpetuated and imperceptibly working its effect through a series of generations, to possess organs capable of examining the bodies it encounters; and the same thing, he asserted, had happened "to all races of gasteropods, in which necessity has induced the habit of touching bodies with some part of their head." He was an advocate also of spontaneous generation, and he believed that all organized beings, from the lowest to the highest forms, were developed progressively from similar living microscopic particles.
He is considered the foremost modern originator of the theory of the variation of species, which Darwin has revived and developed. In 1815-22 appeared Lamarck's chief work, Histoire naturelle des animaux sans vertebres (7 vols. 8vo), by far the most comprehensive treatise on the invertebrata which had appeared, and of which the edition of 1834-'45, with notes by Deshayes and Milne-Edwards, is a standard manual on the subject. His division of the animal kingdom includes three groups, the apathetic, the sensible, and the intelligent. The first comprises infusoria, polyparia, radiaria, and vermes; the second, insecta, arachnida, Crustacea, aunelida, cirri-peda, and mollusca; and the third, pisces, rep-tilia, aves, and mammifera. Some of his statements respecting the habits and functions of the apathetic animals have been disproved by the researches of Ehrenberg and other naturalists. His last work was his Memoires sur les coquilles, published in the Annales du museum, in which he was assisted by Valenciennes, and by his daughter.