ers excepted) only between the
tropics: in receding from the line, they never approach a higher
latitude than the fortieth parallel. The course of the Gulf stream,
however, and the warmth of its water, enable some tropical fish to
extend their habitations far into the temperate zone; thus the chaetodons
which abound in the seas of hot climates, are found among the Bermudas
on the thirty-second parallel, where they are preserved in basins
inclosed from the sea, as an important article of food for the garrison
and inhabitants. Other fish, following the direction of the same great
current, range from the coast of Brazil to the banks of
Newfoundland.[913]

All are aware that there are certain fish of passage which have their
periodical migrations, like some tribes of birds. The salmon, towards
the season of spawning, ascends the rivers for hundreds of miles,
leaping up the cataracts which it meets in its course, and then retreats
again into the depths of the ocean. The herring and the haddock, after
frequenting certain shores, in vast shoals, for a series of years,
desert them again, and resort to other stations, followed by the species
which prey on them. Eels are said to descend into the sea for the
purpose of producing their young, which are seen returning into the
fresh water by myriads, extremely small in size, but possessing the
power of surmounting every obstacle which occurs in the course of a
river, by applying their slimy and glutinous bodies to the surface of
rocks, or the gates of a lock, even when dry, and so climbing over
it.[914] Before the year 1800 there were no eels in Lake Wener, the
largest inland lake in Sweden, which discharges its waters by the
celebrated cataracts of Trolhattan. But I am informed by Professor
Nilsson, that since the canal was opened uniting the river Gotha with
the lake by a series of nine locks, each of great height, eels have been
observed in abundance in the lake. It appears, therefore, that though
they were unable to ascend the falls, they have made their way by the
locks, by which in a very short space a difference of level of 114 feet
is overcome.

Gmelin says, that the Anseres (wild geese, ducks, and others) subsist,
in their migrations, on the spawn of fish; and that oftentimes, when
they void the spawn, two or three days afterwards, the eggs retain their
vitality unimpaired.[915] When there are many disconnected freshwater
lakes in a mountainous region, at various elevatio