This instinct of this fish and other species to go into shallow rivers to deposit their eggs has been made use of by man. At the time of the spawning migration the salmon are taken in vast numbers. The salmon fisheries net over $16,000,000 annually, the shad at least $1,500,000, the smelt fishery nearly $150,000 more. The total annual value of the fisheries of the United States is over $50,000,000. Migration of Fishes. Some fishes change their habitat at different times during the year, moving in vast schools northward in summer and southward in the winter. In a general way such migrations follow the coast lines. Examples of such migratory fish are the cod, menhaden, herring, and bluefish. The migrations are due to temperature changes, to the seeking after food, and to the spawning instinct. Some fish migrate to shallower water in the summer and to deeper water in the winter; here the reason for the migration is doubtless the change in temperature. The herring fisheries have always been a source of wealth to the inhabitants of northern Europe. The banks and shallows of the coast of Newfoundland were undoubtedly known to the Norsemen long before the discovery of this cr untry by Columbus. ow rives number The Problem XXXVI (Optional). The artificial propagation of fishes. (Laboratory Manual, Prob. XXXVI.) The Work of National and State Governments in protecting and propagating Food Fishes. But the profits from the fisheries are steadily decreasing because of the yearly destruction of untold millions of eggs which might develop into adult fish. Fortunately, the government through the Bureau of Fisheries, and various states by wise protective laws and by artificial propagation of fishes, are beginning to turn the tide. Certain days of the week the salmon are allowed to pass up the Columbia unmolested. Closed breeding seasons protect our trout, bass, and other game fish, and also prohibit the catching of fish under a certain size. Many fish hatcheries, both government and state, are engaged in artificially fertilizing millions of fish eggs of various species and protecting the young fry until they can be placed in ponds or streams at a size when they can take care of themselves. This artificial fertilization is usually accomplished by first squeezing out the ripe eggs from a female into a pan of water; in a similar manner the milt or sperm cells are obtained, and poured over the eggs. The fertilized eggs are carefully protected, and, after hatching, the young fry are kept in ideal conditions until later they are shipped, sometimes thousands of miles, to their new home. State and government interposition, however, is in many cases coming too late, for at the present rate of destruction many of our most desirable food fishes will soon be extinct. The sturgeon, the eggs of which are used in the manufacture of the delicacy known as caviare, is an example of a fish that is almost extinct in this part of the world. The shad is found in fewer numbers each year, and in fewer rivers as well. The salmon will undoubtedly soon. meet the fate of other fishes which are taken at the spawning season, unless conservation of a radical sort takes place. Classification of Fishes. The animals we recognize as fishes are grouped by naturalists into four groups: - 1. The Elasmobranchs. - These fishes have a skeleton formed of cartilage which has not become hardened with lime. The gills communicate with the surface of the body by separate openings instead of having an operculum. The skin is rough and the eggs few in number. Sand shark, an elasmobranch. Note the slits leading from the gills. From photograph loaned by the American Museum of Natural History. In some members of this group the young are born alive. Sharks, rays, and skates are elasmobranchs. 2. Ganoids. - The bodies of these are ganoids protected by a series of platelike scales of considerable strength. These fishes are the only remnant of what once was the most powerful group of animals on the earth, the great armored fishes of the Devonian The gar pike is an example. A bony fish. age. 3. The Teleosts, or Bony Fishes. They compose 95 per cent of all living fishes. In this group the skeleton is bony, the gills are protected by an operculum, and the eggs are numerous. Most of our common food fishes belong to this class. 4. The Dipnoi, or Lung Fishes. - This is a very small group, in many respects more like amphibians than fishes, the swim bladder being used as a lung. They live in tropical Africa, South America, and Australia, inhabiting the rivers and lakes there. They withstand drying up in the mud during the dry season, lying dormant for long periods of time in a ball of mud and waking to active life again when the mud coat is removed by immersion in water. REFERENCE BOOKS ELEMENTARY Sharpe, A Laboratory Manual. American Book Company. Davison, Practical Zoology, pages 185-199. American Book Company. ADVANCED Jordan and Evermann, American Food and Game Fishes. Doubleday, Page, and Company. Jordan, Fishes. Henry Holt and Company. Kingsley, Textbook of Vertebrate Zoology. Henry Holt and Company. Riverside Natural History. Houghton, Mifflin, and Company. Amphibia. The Frog Problem XXXVII. Some adaptations in a living frog. (Laboratory Manual, Prob. XXXVII) Adaptations for Life. The most common frog in the eastern part of the United States is the leopard frog. It is recognized by its greenish brown body with dark spots, each spot being outlined in a lighter colored background. In spite of the apparent lack of harmony with their sur roundings, their color, on the contrary, appears to give almost perfect protection. In some species of frogs the color of the skin changes with the surroundings of the frog, another means of protection. Adaptations for life in the water are numerous. The ovoid body, the head merging into the trunk, the slimy covering (for the frog is pro The leopard frog. vided, like the fish, with mucus cells in the skin), and the powerful legs with webbed feet, are all evidences of the life which the frog leads. Locomotion. You will notice that the appendages have the same general position on the body and same number of parts as do your own (upper arm, forearm, and hand; thigh, shank, and foot, the latter much longer relatively than your own). Note that while the hand has four fingers, the foot has five toes, the latter connected by a web. In swimming the frog uses the stroke we all aim to make when we are learning to swim. Most of the energy is liberated from the powerful backward push of the hind legs, which in a resting position are held doubled up close to the body. On land, locomotion may be by hopping or crawling. Sense Organs. The frog is well provided with sense organs. The eyes are large, globular, and placed at the side of the head. When they are closed, a delicate fold, called the nictitating membrane (or third eyelid), is drawn over each eye. Frogs probably see best moving objects at a few feet from them. Their vision is much keener than that of the fish. The external ear (tympanum) is located just behind the eye on the side of the body. Frogs hear sounds and distinguish various calls of their own kind, as is proved by the fact that frogs recognize the warning notes of their mates when any one is approaching. The inner ear also has to do with balancing the body as it has in fishes and other vertebrates. Taste and smell are probably not strong sensations in a frog or toad. They bite at moving objects of almost any kind when hungry. Experience has taught these animals that moving things, insects, worms, and the like, make good food. These they swallow whole, the tiny teeth being used to hold the food. Touch is a welldeveloped sense. They also respond to changes in temperature under water, remaining there in a dormant state for the winter when the temperature of the air becomes colder than that of the water. Breathing. The frog breathes by raising and lowering the floor of the mouth, pulling in air through the two nostril holes. Then the little flaps over the holes are closed, and the frog swallows this air, thus forcing it down into the baglike lungs. The skin is provided with many tiny blood vessels, and in winter, while the frogs are dormant at the bottom of the ponds, it serves as the only organ of respiration. Although we shall take up the study of the internal structure of |