"However, in order to facilitate the study and recognition of these organisms, I give the name of _species_ to every collection of individuals which during a long period resemble each other so much in all their parts that these individuals only present small accidental differences which, in plants, reproduction by seeds causes to disappear. "But, besides that at the end of a long period the totality of individuals of such a species change as the circumstances which act on them, those of these 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 as the result of a long habit of this other mode of existence, and then they constitute a new _species_, which comprehends all the individuals which occur in the same condition of existence. We see, then, the faithful picture of that which happened in this respect in nature, and of that which the observation of its acts can alone discover to us." III. _Lamarck's Views on Species, as published in 1803._ In the opening lecture[171] of his course at the Museum of Natural History, delivered in prairial (May 20-June 18), 1803, we have a further statement of the theoretical views of Lamarck on species and their origin. He addresses his audience as "Citoyens," France still being under the _régime_ of the Republic. The brochure containing this address is exceedingly rare, the only copy existing, as far as we know, being in the library of the Museum of Natural History in Paris. The author's name is not even given, and there is no imprint. Lamarck's name, however, is written on the outside of the cover of the copy we have translated. At the end of the otherwise blank page succeeding the last page (p. 46) is printed the words: _Esquisse d'un Philosophie zoologique_, the preliminary sketch, however, never having been added. He begins by telling his hearers that they should not desire to burden their memories with the infinite details and immense nomenclature of the prodigious quantity of animals among which we distinguish an illimitable number of species, "but what is more worthy of you, and of more educational value, you should seek to know the course of nature." "You may enter upon the study of classes, orders, genera, and even of the most interesting species, because this would be useful to you; but you should never forget that all these subdivisions, which could not, however, be well spared, are artificial, and that nature does not recognize any of them."