1. They all possess either hearts, lungs, brains, nerves, or muscular fibres. It is as yet a controversy among naturalists whether animal life can exist without a brain; but no one has denied muscular fibres, and of course contractility, or excitability, to belong to animal life in all its shapes.
2. They all require more or less air for their existence. Even the snail inhales it for seven months under ground, through a pellicle which it weaves out of slime, as a covering for its body. If this pellicle at any time become too thick to admit the air, the snail opens a passage in it for that purpose. Now air we know acts powerfully in supporting animal life.
3. Many of them possess heat equal to that of the human body. Birds possess several degrees beyond it. Now heat, it was said formerly, acts with great force in the production of animal life.
4. They all feed upon substances more or less stimulating to their bodies. Even water itself, chemistry has taught us, affords an aliment, not only stimulating, but nourishing to many animals.
5. Many of them possess senses, more acute and excitable, than the same organs in the human species. These expose surfaces for the action of external impressions, that supply the absence or deficiency of mental faculties.
6. Such of them as are devoid of sensibility, possess an uncommon portion of contractility, or simple excitability. This is most evident in the polypus. When cut to pieces, it appears to feel little or no pain.
7. They all possess loco-motive powers in a greater or less degree, and of course are acted upon by the stimulus of muscular motion.
8. Most of them appear to feel a stimulus, from the gratification of their appetites for food, and for venereal pleasures, far more powerful than that which is felt by our species from the same causes. I shall hereafter mention some facts from Spalanzani upon the subject of generation, that will prove the stimulus, from venery, to be strongest in those animals, in which other stimuli act with the least force. Thus the male frog during its long connection with its female, suffers its limbs to be amputated, without discovering the least mark of pain, and without relaxing its hold of the object of its embraces.
9. In many animals we behold evident marks of understanding and passion. The elephant, the fox, and the ant exhibit strong proofs of thought; and where is the school boy that cannot bear testimony to the anger of the bee and the wasp?