3142. The animal kingdom accordingly divides into four great districts or circles.
| Circle I. | Intestinal Animals, | Oozoa—Protozoa. |
| II. | Vascular " | Sexual animals—Conchozoa. |
| III. | Respiratory " | Cutaneous " —Ancyliozoa. |
| IV. | Sarcose " | ; Cephalic " —Vertebrata. |
C. ANIMAL CLASSES.
3143. The animal Classes may be designated as the self-substantial representation of a stage in the development of an anatomical system or of the inferior organ of sense, and in the Sarcose animals of these systems themselves or of the cephalic senses.
3144. There are then as many classes as there are stages of development or systems. Thus the intestinal system separates into pharynx or stomach, intestine and absorbents.
3145. The vascular system into veins, arteries, and hearts.
3146. The respiratory system into branchial membrane or skin, into branchiæ, and into lungs or tracheæ, i. e. air-tubes. Taken in a strict sense, such divisions do not constitute classes, as has been already remarked.
3147. It is only the animal systems, which do not divide into several functions, but remaining upon a level with each other, are simply repeated in the higher organs of sense.
First Province. Splanchnozoa, Dermatozoa.
FIRST CIRCLE. INTESTINAL ANIMALS, OOZOA.