quite useless, would it not? But our young Plaice is changing its
appearance very quickly. Its head is growing rather "lopsided." The eye
next the sand is, little by little, brought round to the upper side,
until it looks up instead of down. Its mouth gets a queer one-sided
look, owing to the twisting of the bones in the head.

Many people think that the dark upper part of a flat fish is the back,
and the white under part is the stomach. We have seen, however, that
this is not so, for _flat fish lie on one side_.

For the rest of its life the Plaice will remain flat, with two eyes
looking up, and a twisted head. But its colour alters. The side on which
it lies is white; the upper side becomes brown and speckled, dotted over
with red marks. This is a good disguise. Its enemies cannot distinguish
the Plaice from the pebbles and sand around it. They might swim over it,
and yet not see the thin, flat, brownish body pressed down on the bed of
the sea.

Also, these flat fish have a wonderful way of changing colour. Put them
on light sand, and they become lightish. Put them on dark sand and
pebbles, and they soon match it by becoming brown and mottled. This is a
most useful dodge where so many enemies abound, all swifter in the water
than the slow-swimming flat fish.

If you look for flat fish in an aquarium, you will not easily see them.
Now and again one will swim up, with a wavy motion of its body. On
settling again, it shuffles and flaps about, works itself into the sand,
hiding its edges well under, and then, hey presto! it is gone! If the
flat fish are so hard to find in a tank, you may be sure it would be
impossible to find them on the sea bed. They are poor swimmers, but