1. Intestinal system.
2. Vascular "
3. Respiratory "
4. Osseous "
5. Muscular "
6. Nervous "
3090. That the vegetative systems are correctly arranged after this manner, is proved chiefly by their order of development in the animal series.
3091. The animals, occupying the lowest grade, are nothing but an intestine, which is in many instances scarcely separated or distinct from the tegument; they are devoid of vessels and branchiæ, and are barely provided with self-substantial ovisacs. Their body consists of one or two concentric cysts of an homogeneous and transparent substance—Intestinal animals, Protozoa.
3092. When the intestine is freed from the mass of the body, both then obtain the form and substance of tegumental cysts, whereof the external being only an intestinal tunic, thus represents the peritoneum. They are now, however, united by means of a vascular system, which is again surrounded by a cyst, and thus by a pleura. Their body consists of three concentric cysts; intestine, peritoneum, and pleura. It contains too a liver and self-substantial sexual parts—Vascular animals, Conchozoa.
If these cysts be repeated in the direction of the axis, the tegument becomes an annulated skin. An annulose animal is a multiplied cystic animal. Associated with this character, the respiratory organs are gradually evolved to form vascular plexuses, branchiæ, feet, tracheæ, and wings, while the sexual parts are for the most part separated—Ancyliozoa, Respiratory animals.
3093. The osseous system first appears in the Fishes, along with imperfect, mostly tendonless, and only white muscles, as also a myelon that is only developed into a stunted encephalon, in which the brain-organs of the Thricozoon are in great part wanting.
3094. Typical, or true muscles, provided with tendons, and of a red colour, are first exhibited in the Reptilia.
3095. A complete nervous system, pretty similar to that of the Thricozoa or Pilose animals, having a cerebrum and cerebellum, with similarly distributed and delicate nerves, is first displayed in Birds.
3096. According to the anatomical systems there are, therefore, six divisions of animals:
| A. | Splanchnozoa. | |
| 1. Intestinal animals | Protozoa. | |
| 2. Vascular " | Conchozoa. | |
| 3. Respiratory " | Ancyliozoa. | |
| B. | Sarcozoa. | |
| 4. Osseous animals | Pisces. | |
| 5. Muscular " | Reptilia. | |
| 6. Nervose " | Aves. |