differences, being in some fishes heavy and remaining at the
bottom of the water, in other light and floating on the surface. While
in some species they are distributed separately, in others they adhere
together in masses. The eggs of the salmon, for example, are heavy, hard
and smooth, and deposited separately in a trough dug by the parent and
afterwards covered to prevent them from being carried away by the
stream. In the perch they are adhesive and form long band-like masses of
spawn adhering to water-plants. In the gobies the egg is spindle-shaped,
and attached by one end by means of a network of fibres, resembling
rootlets; while in the smelt the egg is loosely suspended by a membrane
formed by the peeling off of a part of the outer sheath of the capsule.
The eggs of the garfish (_Belone vulgaris_) and of the flying-fish of
the genus _Exocoetus_, attach themselves to foreign objects, or to one
another, by means of threads or cords developed at opposite poles of the
egg.

Among a number of fishes the eggs float at the surface of the sea, often
in enormous masses, when they are carried about at the mercy of tides
and currents. An idea of the size which such masses attain may be
gathered from the fact that the spawn of the angler-fish, _Lophius
piscatorius_, takes the form of a sheet from 2 to 3 ft. wide, and 30 ft.
long. Another remarkable feature of these floating eggs is their
transparency, inasmuch as they are extremely difficult to see, and hence
they probably escape the rapacious maws of spawn-eating animals. The cod
tribe and flat-fishes lay floating eggs of this description.

The maximum number of eggs laid by fishes varies greatly, some species
laying relatively few, others an enormous number. But in all cases the
number increases with the weight and age of the fish. Thus it has been
calculated that the number laid by the salmon is roughly about 1000 to
every pound weight of the fish, a 15 lb. salmon laying 15,000 eggs. The
sturgeon lays about 7,000,000; the herring 50,000; the turbot
14,311,000; the sole 134,000; the perch 280,000. Briefly, the number is
greatest where the risks of destruction are greatest.

The eggs of the degenerate fishes known as the lampreys and hag-fishes
are remarkable for the fact that in the latter they are large in size,
cylindrical in shape, and provided at each end with hooklets whereby
they adhere one to another; while in the lampreys they are extremely
small and embedded in a