24. Between the vegetable and animal kingdom there are no distinctly traced boundaries. Upon the borders of the two are the zoophytes, or animal plants, of which the name indicates that they belong to both: they are the hyphen between the two.
Like animal, plants are born, live, grow, are nourished, breathe, reproduce their kind, and die. Like them they have need of light, heat, and water; if they are deprived of them, they wither and die. The absorption of vitiated air and deleterious substances poisons them. Their distinctive trait of character, the most defined, is of being attached to the soil, and, without leaving their place, drawing their nourishment from it.
The zoophyte has the exterior appearance of a plant. Like the plant it belongs to the soil, but seems to partake more of the nature of an animal. It draws its nourishment from the ambient midst.
An animal, being one degree above a zoophyte, is free to go and seek its food. Firstly, there are innumerable varieties of polyps with gelatinous bodies, without very distinct organs, and which differ from plants only by locomotion. Then come in the order of development those with organs of vital activity and instinct, — intestinal worms, mollusks, fleshly animals without bones, of which some are entirely destitute, as slugs or cuttle-fish; others are provided with shells, as snails and oysters; then shell-fish, of which the skin is invested with a hard shell, like crabs and lobsters; insects, who lead a very active life, and manifest an industrious instinct, like the ant, the bee, and the spider; a few submit themselves to a metamorphosis, as the caterpillar, which is transformed into an elegant butterfly. Then comes the order of vertebrates, — animals with a bony framework, — which comprises fish, reptiles, birds, and mammals, of which the organization is more complete.