his profound insight, sound judgment, and philosophic breadth. The reforms that he brought about in the classification of the invertebrate animals were direct and positive improvements, were adopted by Cuvier in his _Règne animal_, and have never been set aside. We owe to him the foundation and definition of the classes of Infusoria, Annelida, Arachnida, and Crustacea, the two latter groups being separated from the insects. He also showed the distinctness of echinoderms from polyps, thus anticipating Leuckart, who established the phylum of Coelenterata nearly half a century later. His special work was the classification of the great group of Mollusca, which he regarded as a class. When in our boyhood days we attempted to arrange our shells, we were taught to use the Lamarckian system, that of Linné having been discarded many years previous. The great reforms in the classification of shells are evidenced by the numerous manuals of conchology based on the works of Lamarck. We used to hear much of the Lamarckian genera of shells, and Lamarck was the first to perceive the necessity of breaking up into smaller categories the few genera of Linné, which now are regarded as families. He may be said to have had a wonderfully good eye for genera. All his generic divisions were at once accepted, since they were based on valid characters. Though not a comparative anatomist, he at once perceived the value of a knowledge of the internal structure of animals, and made effective use of the discoveries of Cuvier and of his predecessors--in fact, basing his system of classification on the organs of respiration, circulation, and the nervous system. He intimated that specific characters vary most, and that the peripheral parts of the body, as the shell, outer protective structures, the limbs, mouth-parts, antennæ, etc., are first affected by the causes which produce variation, while he distinctly states that it requires a longer time for variations to take place in the internal organs. On the latter he relied in defining his classes. One is curious to know how Lamarck viewed the question of species. This is discussed at length by him in his general essays, which are reproduced farther on in this biography, but his definition of what a species is far surpasses in breadth and terseness, and better satisfies the views now prevailing, than that of any other author. His definition of a species is as follows: "Every collection of similar individuals, perpetuated by generation in the same condition, so long as the circumstances of their situation do not change enough to produce variations in their habits, character, and form."