Fish inhabit all kinds of water, the sea, rivers, and ponds, and many which live habitually in the sea come into rivers at certain seasons; and with respect to those which dwell always in the sea, some inhabit certain tracts only, and confine themselves to them, just as quadrupeds do to certain localities on the land. It has been a matter of wonder how the Fish get into ponds formed by the drainage of lands; but most ponds are supplied by springs which run underground from adjacent lakes or rivers, or by rills running on the surface, these bring the ova or eggs, which in favourable situations become hatched. Fish are exceedingly prolific, the eggs in the roe of a Codfish were estimated by Lewenhoec, to be upwards of 9,000,000, but not one in a thousand comes to maturity; there are enemies on all sides to devour them before they are hatched, and others to attack them afterwards. Some of the rivers of France have lately been artificially stocked with Fish by causing the fecundated spawn to be preserved till they are of a bulk and strength to protect themselves. This was effected by confining them in tanks floating in the water and perforated with holes, and afterwards placing them in a part of the river, inclosed both above and below by means of nets, so as to keep away their enemies--the larger Fishes. Fishes were the first of the Vertebrated animals created, and as a proof of the incorrectness of the doctrine of development, these first-created Fish were of a class corresponding to the most highly organised Fishes of the present day. Fishes are divided into two families: 1, Osseous Fishes (with a bony skeleton); 2, Cartilaginous Fishes (with a cartilaginious skeleton). The Osseous Fishes are divided into six Orders:-- 1. ACANTHOPTERYGII (Thorny-fin). [Illustration: FIG. 37.--1, PERCH (Perea fluvia ilis). 2, MACKEREL (Scomber vulgaris). 3, GURNARD (Trigla Gurnhardus).] The Acanthopterygii include a great number of our ordinary useful Fishes, as Mackerel, Perch, Tunny, Gurnard, &c. (fig. 37). The Perch is a good example of this order, the sharp spines on its dorsal fin being well developed, and dangerous for anglers to handle. 2. MALACOPTERYGII ABDOMINALES (Abdominal soft-fin). The abdominal Malacopterygii include the Pilchard, Herring, Pike (fig. 38), Salmon (fig. 39), Anchovy, Trout, Roach, Chub, Tench, and many more of the Fish which inhabit our streams and the sea. [Illustration: FIG. 39.--THE SALMON (Salmo salar).]