Fishes, we know, have very little red blood; reptiles are cold-blooded animals; but whales have plenty of warm, red blood. They are very strong and active creatures in spite of their unwieldy size. The lightness afforded by their blubber, or sheath of fat, and the large amount of air they can contain in their great lungs, and the strength of the tail with its wide flukes,[80] enable them to dash through the water with amazing swiftness. Most of the “true whales” are flesh-eaters, with very fierce appetites. They devour fishes, mollusks, crustaceans, and even seals or other whales. They need enormous quantities of food to support such large bodies, for a Greenland sperm whale is sometimes seventy feet long, and from twenty to thirty feet thick through the shoulders. To secure the needed amount of food, the vast mouth opens wide. In some whales a man can stand upright between the extended jaws. In the “right whale,” which has no teeth, the mouth is lined along the upper jaw with long, narrow plates or flakes called baleen, of which whalebone is made. Every piece of whalebone is a strip of this baleen, from within the mouth of a right whale, and every such piece has a wonderful history behind it, for it has been floating, perhaps for many years, through the cold Arctic seas. It could tell us rare tales if it could speak. These plates of baleen are sometimes seven yards long, and the mouth of one whale has about seven hundred plates. The chief food of this right, or whalebone whale, consists of very small brown crustaceans, one of the numerous crab family. These creatures are so abundant in the northern seas that they lie in banks many leagues long and several feet thick. The whale feeds on these beds of living animals, as a cow browses on grass or hay. Whales are mild and inoffensive in disposition, unless greatly irritated by wounds and attack. They seldom quarrel among themselves, but are playful and affectionate, while the mother shows intense fondness for her young. Whales are social animals, and go in herds, or groups; one is seldom found alone. In the spring the whales pair, and move off together to find some place where they may rear their young. As they travel together they seem very lively and happy; they stop to feed, and indulge in frolics, leaping out of the water, tumbling over and over each other, turning somersaults, and striving to show what they can do. As they come to inlets or deep, quiet bays, which may afford them a safe home, the male whale goes to explore their fitness, or to see if the spot is already taken by some other couple. This is the spring house-hunting of this famous family, and while Mr. Whale enters to make inquiries, Mrs. Whale waits outside. Finally, an abode is selected, and here the mother remains, until in autumn, one, or at most two, little baby whales are born. Compared with their big mother they are small, but compared with human children they are giants.