. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. THE FISHES 277 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 Nors
. Elements of biology; a practical text-book correlating botany, zoology, and human physiology. Biology. THE FISHES 277 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 country by Columbus. Classification of Fishes. — The animals we recognize as fishes are grouped by naturalists into four groups:. Sand shark, an elasmobranch. Note the slits leading from the gills. From photograph loaned by the American Museum of Natural History. 1. The Elasmobranchs. — These fishes have a skeleton formed of carti- lage 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. In some members of this group the young are born alive. Sharks, rays, and skates are Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original Hunter, George William, 1873-1948. New York, American book company
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