Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . simply that the anatomy of this immense assemblageof low-organised animals is not yet sufficiently understood ; and, con-sequently, general propositions, and at the same time positive ones,like those which define the Vertebrate, Molluscous, and Articulatesub-kingdoms, cannot be enunciated. Much has unquestionably been done in this field of NaturalHistory since the time of Cuvier, and attempts have been made, withvarious degrees of success, to subdivide the Radiata accor
Lectures on the comparative anatomy and physiology of the invertebrate animals : delivered at the Royal College of Surgeons . simply that the anatomy of this immense assemblageof low-organised animals is not yet sufficiently understood ; and, con-sequently, general propositions, and at the same time positive ones,like those which define the Vertebrate, Molluscous, and Articulatesub-kingdoms, cannot be enunciated. Much has unquestionably been done in this field of NaturalHistory since the time of Cuvier, and attempts have been made, withvarious degrees of success, to subdivide the Radiata according topositive characters. The binary division, which I proposed in 1835 f, was founded onthe following considerations. The Radiata of Cuvier, in w^hich thenervous system could be most unequivocally traced in a filamentaryform, present an alimentary canal as a distinct tube, with a mouth * Eirst demonstrated by Hunter, in the Crustaceans and Insects. See Treatiseon the Blood, p. 174., and X. vol. ii. p. 138. plxvii. t Syllabus of the Lectures on Comparative Anatomy, given at the MedicalSchool of St. Bartholomews. CLASSIFICATION OF ANIMALS. 15 and anus, suspended in a distinct abdominal cavity : the well-definednerves govern a corresponding development of the muscular is by impregnated ova, rarely by spontaneous fission orgemmation. The Echinodermata, Rotifera^ Ccelehnmtha, and Bryo-zoa, are the classes of Cuviers zoophytes, which were groupedtogether by positive characters, under the title Nematoneura. But a filamentous condition of the nervous system is not to be de-nied in the rest of the zoophytes; each day brings with it testimonyof its presence in animalcules, where it had not before been , in those classes in which the condition of the nervoussystem is most obscure, we find that the digestive cavity is generallyexcavated in the common parenchyma of the body, is devoid of freeparietes, and seldom has an anal outlet: particular
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