is said, I
know not how truly, that the young fry will stroll out for an
occasional swim on their own account, but will return at any threat of
danger to their father's bosom, for a considerable time after the
first hatching. This is just like what one knows of kangaroos and many
other pouched mammals, where the mother's pouch becomes a sort of
nursery, or place of refuge, to which the little ones return for
warmth or safety after every excursion.

[Illustration: NO. 7. POUCH OF PIPE-FISH.]

The sea-horses and many other fish have similar pouches; but, oddly
enough, in every case it is the male fish which bears it, and which
undertakes the arduous duty of nurse for his infant offspring.

A few female fish, on the other hand, even hatch the eggs within their
own bodies, and so apparently bring forth their young alive, like the
English lizard among reptiles. This, however, is far from a common
case: indeed, in an immense number of instances, neither parent pays
the slightest attention to the eggs after they are once laid and got
rid of: the spawn is left to lie on the bottom and be eaten or spared
as chance directs, while the young fry have to take care of
themselves, without the aid of parental advice and education. But
exceptions occur where both parents show signs of realizing the
responsibilities of their position. In some little South American
river fish, for instance, the father and mother together build a nest
of dead leaves for the spawn, and watch over it in unison until the
young are hatched. This case is exactly analogous to that of the doves
among birds: I may add that wherever such instances occur they always
seem to be accompanied by a markedly gentle and affectionate nature.
Brilliantly-coloured fighting polygamous fishes are fierce and cruel:
monogamous and faithful animals are seldom bright-hued, but they mate
for life and are usually remarkable for their domestic felicity. The
doves and love-birds are familiar instances.

Frogs are very closely allied to fish: indeed, one may almost say that
every frog begins life as a fish, limbless, gill-bearing, and aquatic,
and ends it as something very like a reptile, four-legged,
lung-bearing, and more or less terrestrial. For the tadpole is
practically in all essentials a fish. It is not odd, therefore, to
find that certain frogs reproduce, in a very marked manner, the
fatherly traits of their fish-like ancestors. There is a common kind
of frog in France, Be