n as
the 'plated' sea-slugs--so called from the overlapping stony plate borne
on the back--the young are housed in a nursery on the back of the
mother, the plate referred to serving as a roof (see fig. 1). In another
of the sea-slugs the young cling to the skin of the mother until they
are big enough to shift for themselves.

In all these cases, you will notice, the extraordinary forms taken by
their unprotected relatives during early life are dispensed with. The
reason of this is clear after a moment's reflection. The peculiar shapes
which we described earlier are so many special devices designed to aid
the young in gaining a living until their full-grown shape has been
developed. But when these are specially sheltered in nurseries, they
have nothing to do but grow, for their food is brought to them.

The higher we search in the scale of animal life, the more numerous and
striking become the instances of the love and care shown by parents for
their children. Among the fishes and the frogs and toads, for example,
there are such wonderful instances of this that we must deal with each
of these groups separately.

When we come to birds and mammals, we find it hard indeed to select
instances, because, with but few exceptions, these creatures are most
exemplary parents. Let us take, by way of example, one or two cases
among the mammals.

The ponderous hippopotamus carries her young one on her back when
swimming, to save it from the jaws of the hungry crocodile. Some of the
opossum family are remarkable for devotion to their young: one species,
for example, though considerably smaller than a cat, cheerfully carries
her large family about on her back, though each of them is as large as a
full-grown rat! They maintain themselves in perfect safety, while the
mother climbs about the trees, by twisting their long tails around
hers, which is purposely turned forward over her back after the fashion
shown in our illustration (fig. 4). Bats, again, undertake what almost
seem impossible burdens, for the mother, though she has to obtain all
her food when on the wing, refuses to leave her young one, as would seem
but natural, in some place of safety, but carries it with her wherever
she goes. The little mite clings tightly to the soft fur of the under
side of the body (fig. 5). In some cases as many as four baby bats are
carried in this way at a time!

[Illustration: Fig. 1.--Sea-slug, with young.]

[Illustration: Fig. 2.--Sea-urc