. Comparative zoology, structural and systematic : for use in schools and colleges. Zoology; Anatomy, Comparative; Physiology, Comparative. HOW ANIMALS MOVE. 159 vertical, and single. The former, called pectoral and ven- tral fins, represent the fore and hind limbs of Quadrupeds. The vertical fins, which are only expansions of the skin, vary in number; but in most Fishes there are at least three: the caudal, or tail-fin; the dorsal, or back-fin; and the anal, situated on the abdomen, near the tail. The chief locomotive agent is the tail, which sculls like a stern-oar; the other fins are mainly
. Comparative zoology, structural and systematic : for use in schools and colleges. Zoology; Anatomy, Comparative; Physiology, Comparative. HOW ANIMALS MOVE. 159 vertical, and single. The former, called pectoral and ven- tral fins, represent the fore and hind limbs of Quadrupeds. The vertical fins, which are only expansions of the skin, vary in number; but in most Fishes there are at least three: the caudal, or tail-fin; the dorsal, or back-fin; and the anal, situated on the abdomen, near the tail. The chief locomotive agent is the tail, which sculls like a stern-oar; the other fins are mainly used to balance and raise the body. When the two lobes of the tail are equal, and the vertebral column stops near its base, as in the Trout, it is said to be homocercal. If the vertebra extend into the upper lobe, making it longer than the lower one, as in the Shark, the tail is called hetero-. cercal. The latter is the more effec- tive for varying the course; the will accompany and Fig. 124.—Diagram illustrat- ing the locomotion of a Fish. The tail describes the arc of an ellipse; the resultant of the two im- pulses is the straight line in front. Shark, e. g., will accompany gambol around a ship in full sail across the Atlantic. The Whale swims by striking the water up and down, instead of laterally, with a fin-like horizontal tail. Many air-breathing animals swim with facility on the surface, as the Water-birds, having webbed toes, and most of the Reptiles and Quadrupeds. (2) Locomotion in Air.—The power of flight requires a special modification of structure and an extraordinary muscular effort, for air is 800 times lighter than water. Nevertheless, the velocity attainable by certain Birds is greater than that of any Fish or Quadruped; the Hawk being able to go at the rate of 150 miles an hour. The bodies of Insects and Birds are made as light as possible by the distribution of air-sacs or The wings of Insects are generally four in number;. Please note th
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectzoology, bookyear1883
