Page:Natural History, Fishes.djvu/68

54 flexible one; a large portion of the remainder have the division indicated by a depression in the margin, or a cleft more or less deep, though the membrane is continuous. In some cases, as already intimated, the first dorsal is represented by a few detached spines, either quite destitute of membrane, or each furnished with its own.

In some of the Gurnards one or more of the spinous rays are greatly prolonged beyond the membrane; in the Dory the membrane is prolonged between the spines into lengthened threads; in the Sword-fish, the Opah, and the Gemmeous Dragonet, the anterior portion is elevated like a sail; while in the singular genus Pteraclis, of the American seas, figured on the opposite page, both the dorsal and the anal are so immense as to give to the vertical outline of this fish somewhat the form of a butterfly with expanded wings. The Gurnards have the pectorals unusually developed, so that some foreign species can use them as organs of flight through the air. Examples of this, in a less degree, may be observed in our native species,