Page:Natural History, Fishes.djvu/23

Rh which are endowed with swiftness in swimming, the tail-fin is forked, each division being pointed, as are also the pectorals; while in those of sluggish habits, the caudal, as well as the pectorals, is commonly short, even, or rounded. It is by the force of the powerful strokes given obliquely right and left upon the water by this fin that the

fish is urged onward in swift swimming; the pectorals and ventrals seem little used to communicate motion, except it be in deliberate change of place, for very short distances, or for turning; their chief use seems to be that of balancing the body.

The bones are less dense and compact in their structure than those of the preceding Classes;