The Outline of Science, Volume 1

The three-spined and two-spined sticklebacks live equally well in fresh or salt water; the larger fifteen-spined stickleback is entirely marine. In all three species the male fish makes a nest, in fresh or brackish water in the first two cases, in shore-pools in the third case. The little species use the leaves and stems of water-plants; the larger species use seaweed and zoophyte. The leaves or fronds are entangled together and fastened by glue-like threads, secreted, strange to say, by the kidneys. It is just as if a temporary diseased condition had been regularised and turned to good purpose. Going through the nest several times, the male makes a little room in the middle. Partly by coercion and partly by coaxing he induces a female—first one and then another—to pass through the nest with two doors, depositing eggs during her short sojourn. The females go their way, and the male mounts guard over the nest. He drives off intruding fishes much bigger than himself. When the young are hatched, the male has for a time much to do, keeping his charges within bounds until they are able to move about with agility. It seems that sticklebacks are short-lived fishes, probably breeding only once; and it is reasonable to suppose that their success as a race depends to some extent on the paternal care. Now if we could believe that the nesting behaviour had appeared suddenly in its present form, we should be inclined to credit the fish with considerable mental ability. But we are less likely to be so generous if we reflect that the routine has been in all likelihood the outcome of a long racial process of slight improvements and critical testings. The secretion of the glue probably came about as a pathological variation; its utilisation was perhaps discovered by accident; the types that had wit enough to take advantage of this were most successful; the routine became enregistered hereditarily. The stickleback is not so clever as it looks. Photo: Imperial War Museum. HOMING PIGEON A blue chequer hen, which during the War (in September of 1918) flew 22 miles in as many minutes, saving the crew of an aeroplane in difficulties. Photo: Imperial War Museum. CARRIER PIGEON Carrier pigeons were much used in the War to carry messages. The photograph shows how the message is fixed to the carrier pigeon's leg, in the form of light rings. Photo: James's Press Agency. YELLOW-CROWNED PENGUIN Notice the flightless wings turned into flippers, which are often flapped very vigorously. The very strong feet are also noteworthy. Penguins are mostly confined to the Far South. Photo: Cagcombe & Co. PENGUINS ARE "A PECULIAR PEOPLE" Their wings have been turned into flippers for swimming in the sea and tobogganing on snow. The penguins come back over hundreds of miles of trackless waste to their birthplace, where they breed. When they reach the Antarctic shore they walk with determination to a suitable site, often at the top of a steep cliff. Some species waddle 130 steps per minute, 6 inches per step, two-thirds of a mile per hour. [Pg 213]