Of these we will take first the family _Salmonidæ_, of which the Salmon (_Salmo salar_), and the Smelt (_Osmerus eperlanus_) are well-known examples. Several species of the family are remarkable for their periodical migrations from fresh to salt water or _vice versa_, and we cannot do better than briefly relate the interesting life-history of the salmon as a striking instance of these peculiar wanderings. This fish quits the sea at the close of the summer, and ascends the rivers for the purpose of depositing its spawn, the colder water of the rivers being necessary for the development of the young. Its upward journey is beset with many difficulties, for it has to shoot the various rapids and leap the cascades, the latter often demanding the most prodigious efforts on the part of the fish, which frequently leaps several feet out of the water, and even then has sometimes to renew its attempts over and over again before it finally succeeds. Indeed, the difficulties to be overcome are so numerous that the fish often reaches the goal in such an exhausted condition that it would hardly be recognised as the salmon by those who have only seen it in the prime condition in which it is captured during its return to the sea in the following spring or summer. The male, at this period called the _kipper_, is of a dull red colour, irregularly blotched with yellow and light brown, and its skin is covered with a slimy secretion. Its body is lean, and the head, now large and out of all proportion, is rendered still more unsightly by the protrusion of the lower jaw, which at this season, when the males are particularly pugnacious, becomes a formidable weapon of offence. The condition of the female, now called the _baggit_, is equally poor, and the skin has changed its bright silvery colour for dark and dingy shades. The female digs a nest in the form of a deep trench by wriggling her body in the gravel of the bed of the stream, and there deposits her eggs, many thousands in number, small quantities at a time. As each batch is deposited the eggs are fecundated by the kipper, and then covered over lightly with gravel by the baggit; and this work having been accomplished, both male and female rest and feed, with the result that their condition is rapidly improved.