Page:The Scientific Monthly vol. 3.djvu/607

Rh

OLLOWING the pro-fishes of Odrovician time (p. 508) the great group of fishes begins its evolution with (A) active, free-swimming, double pointed types of fusiform shape, adapted to rapid motion through the water and to predaceous habits in pursuit of swift-moving prey. From this type there radiated many others: (B) the deep, narrow-bodied fishes of relatively slow movements, frequenting the middle

depths of the waters; (D) the swift-moving, elongate types which increasingly depended upon lateral motions of the body for propulsion and thus tended to lose the lateral fins and finally to assume an elongate, eel shape entirely finless; (C) other bottom-living forms in which the body became laterally flattened, the head very large relatively and covered with protective dermal armature, the movements of the animals very slow.