alluded to his division of the Animal Kingdom into the Apathetic, Sensitive, and Intelligent animals.  The Apathetic were those devoid of all sensitiveness except when aroused by the influence of some external agent.  Under this head he placed five classes, including the Infusoria, Polyps, Star-Fishes, Sea-Urchins, Tunicata, and Worms,—­thus bringing together indiscriminately Radiates, Mollusks, and Articulates.  Under the head of Sensitive he had also a heterogeneous assemblage, including Winged Insects, Spiders, Crustacea, Annelids, and Barnacles, all of which are Articulates, and with these he placed in two classes the Mollusks, Conchifera, Gasteropoda, and Cephalopoda.  Under the head of Intelligent he brought together a natural division, for he here united all the Vertebrates.  He succeeded in this way in making out a series which seemed plausible enough, but when we examine it, we find at once that it is perfectly arbitrary; for he has brought together animals built on entirely different structural plans, when he could find characters among them that seemed to justify his favorite idea of a gradation of qualities.  Blainville attempted to establish the same idea in another way.  He founded his series on gradations of form, placing together, in one division, all animals that he considered vague and indefinite in form, and in another all those that he considered symmetrical.  Under a third head he brought together the Radiates; but his symmetrical division united Articulates, Mollusks, and Vertebrates in the most indiscriminate manner.  He sustained his theory by assuming intermediate groups,—­as, for instance, the Barnacles between the Mollusks and Articulates, whereas they are as truly Articulates as Insects or Crabs.  Thus, by misplacing certain animals, he arrived at a series which, like that of Lamarck, made a strong impression on the scientific world, till a more careful investigation of facts exposed its fallacy.

Oken, the great German naturalist, also attempted to establish a connected chain throughout the Animal Kingdom, but on an entirely different principle; and I cannot allude to this most original investigator, so condemned by some, so praised by others, so powerful in his influence on science in Germany, without attempting to give some analysis of his peculiar philosophy.  For twenty years his classification was accepted by his countrymen without question; and though I believe it to be wrong, yet, by the ingenuity with which he maintained it, he has shed a flood of light upon science, and has stimulated other naturalists to most important and interesting investigations.  This famous classification was founded upon the idea that the system of man, the most perfect created being, is the measure for the whole Animal Kingdom, and that in analyzing his organization we have the clue to all organized beings.  The structure of man includes two systems of organs:  those which maintain the body in its integrity, and which he shares in some sort with the lower animals,—­the