Always inhabiting the waters; fish are swift in their motion and voracious in their appetites. They breathe by means of gills, which are generally united by a bony arch; swim by means of radiate fins, and are mostly covered over with cartilaginous scales. Besides the parts they have in common with other animals, they are furnished with a nictitant membrane, and most of them with a swim-bladder, by the contraction or dilatation of which, they can raise or sink themselves in their element at pleasure.

A very numerous and various class consisting of small animals, breathing through lateral spiracles, armed on all sides with a bony skin, or covered with hair; furnished with many feet, and moveable antennae (or horns), which project from the head, and are the probable instruments of sensation.

Animals of slow motion, soft substance, able to increase their bulk and restore parts which have been destroyed, extremely tenacious of life, and the inhabitants of moist places. Many of them are without a distinct head, and most of them without feet. They are principally distinguished by their tentacles (or feelers). By the Ancients they were not improperly called imperfect animals, as being destitute of ears, nose, head, eyes and legs; and are therefore totally distinct from Insects.

Animals that are distinguished by a body cold and generally naked; stern and expressive countenance; harsh voice; mostly lurid color; filthy odor; a few are furnished with a horrid poison; all have cartilaginous bones, slow circulation, exquisite sight and hearing, large pulmonary vessels, lobate liver, oblong thick stomach, and cystic, hepatic, and pancreatic ducts: they are deficient in diaphragm, do not transpire (sweat), can live a long time without food, are tenacious of life, and have the power of reproducing parts which have been destroyed or lost; some undergo a metamorphosis; some cast (shed) their skin; some appear to live promiscuously on land or in the water, and some are torpid during the winter.