Suddenly the dim outlines of the whale took shape in the green depths far below me but when near the surface the animal checked its upward rush, turned downward, and dove directly under the ship, rising a hundred fathoms away on the port beam. I could see every movement of the great body as clearly as though the whale had been suspended in mid-air. When the animal turned, the side fins were thrown outward but were pressed close to the body as it swam under the ship.
Posterior view of a blue whale on the slip at Aikawa, Japan. The flukes have been cut off and the wide thin caudal portion of the body is well shown.
A whale’s flippers must not be compared with the fins of a fish, for in structure the two are quite unlike. The flippers of all cetaceans are merely the fore-limbs of ordinary land mammals, which have become overlaid with blubber to form a paddle in adaptation to an aquatic life and have the bones, blood vessels, and nerves of the human arm. The flipper of the humpback whale has four greatly elongated fingers but in some other species there are five fingers as in the human hand.
Cetaceans also have rudiments of the hind-limbs. These consist of the pelvis, which is fairly well developed, and small nodules of bone representing the femur and sometimes the tibia; the latter is cartilaginous except in rare cases. These rudiments are, of course, entirely concealed within the body and can only be found by carefully cutting away the flesh surrounding the sexual organs.
The flipper of a humpback whale. “The flippers of all cetaceans are merely the fore-limbs of ordinary land mammals, which have become overlaid with blubber to form a paddle.”
One of the most striking things about the blue whale, and indeed all its relatives, are the folds which extend longitudinally from the lower jaw backward over the throat, breast, and abdomen. In different species of whales the folds vary in number and width, the furrows between them being about an inch in depth and the skin capable of great extension.
The use of the folds has been a subject of disagreement among naturalists, but my own belief is that they are an adaptation to increase the mouth capacity and to give greater power of expansion to the lungs.
