ZOOPHYTOLOGY, (from an animal, CpUTOV a plant, and xoyos a discourse) is that branch of na tural history which treats of zoophytes, or animals of a plant-like form.
Although the term zoophyte is usually confined to those ramified, fixed, compound animals com posing the second lowest class, we shall avail our selves of the more extended sense in which the term is used by Cuvier, to lay before our readers in the present article a brief systematic view of the four classes, Entozoa, Radiata, Zoophyta and In fusoria, which that distinguished naturalist has comprehended under this term. The great division of the animal kingdom composed of these four classes is called Radiata by Cuvier, from the ani mals exhibiting very often a radiated form of the whole body, or of some of its parts. The same general character is expressed by the term Actino zoaires (from radius, and fmOr animal) more recently applied to this division by Jilainville. These animals formed only a part of Linnxus's great class Vermes. They are termed Apathica by Lamarck, from their being all destitute of organs of sense and even of nerves, and from his con sidering their motions to be mere automatic phe nomena not accompanied with feeling. They form the division called Acephala by Latreille from their having no part analogous to the head of the arti culated classes. From the Acalepha downwards are comprehended under Dr. Grant's division Aneurosa, so named from their exhibiting no trace of nervous filaments.
The external form of the animals belonging to this great division is infinitely more diversified, and often much more complicated than that of the higher classes, but they possess a more simple or ganization, and have fewer functions to perform. They possess no red blood nor internal articulated skeleton, nor brain, nor spinal marrow, nor heart, nor pulsating dorsal vessel, nor a complete circu lation, nor glands for secretion. The Entoza alone exhibit longitudinal nervous filaments like those of Cuvier's Articulata, or Dr. Grant's Neurosa.
The nerves in the Radiata radiate from ganglia placed around the ccsophagus, as in the Mollus cous or Gangliated classes. A partial circulation is observed only in these two classes. The respira tion is partial and aquatic, and is effected by or gans which ramify through the body like air-ves sels of articulated animals. The muscular fibres are distinct in the Entozoa, but scarcely discernible in the inferior classes. The skeleton is often in ternal, but more frequently external. None pos sess articulated organs for locomotion. Organs of generation and a distinction of sex have been ob served only on a very few of the Entozoa. In the other classes all the individuals are alike capable of reproduction, and their mode of generation is either gemmiparous or fissiparous. Latreille has been misled by the erroneous observations of Spix to consider the reproductive gemmules of these animals as similar to the ova of the higher classes. The development of the so-named ova of the ra diated animals has not yet been satisfactorily ob served, but it is known that some of them possess spontaneous motion when newly separated from the parent, as in the gemmules of zoophytes. The Entozoa have generally a lengthened serpentine form, the Radiata are circular and depressed, the Zoophytes are ramified, and the Infusoria approach to the spherical form. The Entozoa are small, white, soft, naked animals, found only in the bodies of other animals. The Radiata are found creeping at the bottom of the sea, or floating in myriads upon the waves. The Zoophytes decorate with their elegant arborescent forms every thing which lies beneath the surface of the ocean; they prefer the calm recesses of the deep, and hang in count less numbers from the roofs of submarine caves. The Infusoria abound wherever there is moisture on this planet, whether exposed to the atmosphere, as in rivers, lakes and the ocean, or shut up in the bodies of animals or plants.