Page:Natural History, Fishes.djvu/19

Rh they could not sink, and make off. It is, however, a curious subject for inquiry."

The Diodon, as is well known, has the habit of inflating its body with air, and of floating helplessly in this condition at the surface; but in this case it appears that the air is not taken into the bladder, but into the huge stomach, filling the cavity of the abdomen.

"A Gold-fish, in a small fountain, in the grounds of a gentleman of my acquaintance, swam about for more than two months, with its belly upwards. It appeared perfectly healthy and lively. This change from the natural position of the fish was, probably, owing to an enlargement or defect in the air-bladder."

In conformity with their structure, the sphere of activity of Fishes is the water. The Flying-fishes, and some of the Gurnards, are able to elevate themselves into the air, and to maintain their position there for a few seconds; and some of the Frog-fishes and Eels can crawl upon the exposed mud or sand, during the hours that intervene between the ebb and flow of the tide; but these exceptions scarcely break the universality of the law which confines Fishes to the water. There is, however, considerable diversity in the locality assigned to different species; some inhabit fresh-waters only, some only the sea; others are able to exist in both, either by periodical migration, or at pleasure. Of fresh-water Fishes, some inhabit large rivers, others small streams; rapid and sluggish waters have each charms for some: great inland lakes possess peculiar species, and some are found only in the