less than the mole, has altogether lost the use of sight: so that it shows nothing more than vestiges of this organ." Lamarck described speciation as follows: as new modifications will necessarily continue to operate, however slowly, not only will there continually be found new species, new genera, and new orders, but each species will vary in some part of its structure and form ... individuals which from special causes are transported into very different situations from those where the others occur, and then constantly submitted to other influences – the former, I say, assume new forms, and then they constitute a new species. He argued that gaps between differing kinds of animals resulted from the extinction of intermediate forms, in: a branching series, irregularly graduated which has no discontinuity in its parts, or which, at least, if its true that there are some because of lost species, has not always had such. It follows that the species that terminate each branch of the general series are related, at least on one side, to the other neighboring species that shade into them. Lamarck proposed the transmutation of species ("transformisme"), but did not believe that all living things shared a common ancestor. Rather he believed that simple forms of life were created continuously by spontaneous generation. He also believed that an innate life force, which he sometimes described as a nervous fluid, drove species to become more complex over time, advancing up a linear ladder of complexity similar to the mediaeval great chain of being. Contents The first volume concerns natural history, the second physiology, and the third psychology. Page numbers are given in parentheses. VOLUME 1 Avertissement (I–XXV) Discours Préliminaire (1) Première Partie (Considérations sur l'Histoire naturelle des Animaux, leurs caractères, leurs rapports, leur organisation, leur distribution, leur classification et leur espèces) I. Des Parties de l'art dans les productions de la Nature (17) II. Importance des Rapports (39) III. De l'Espèce parmi les Corps vivans, et de l'idée que nous devons attacher à ce mot (53) IV. Généralités sur les Animaux (82) V. Sur l'Etat actuel de la Distribution et de la Classification des Animaux (102) VI. Dégradation et simplification de l'organisation d'une extrémité a l'autre de la Chaîne animale (130) VII. De l'influence des Circonstances sur les actions et les habitudes des Animaux, et de celle des actions et des habitudes de ces Corps vivans, comme causes qui