Put a Salmon and a Plaice side by side, and it is plain that they live in very different ways.  One is made to dart like an arrow, the other to lie flat.  One is the shape of a torpedo, the other is flat like a raft.  The shape and colour of the Plaice tell their own story of a life on the sandy, pebbly bed of the sea.  And look at the eyes!  Both are on the upper side of the head!  What could be better for a fish that lies flat on the ocean floor?

The Plaice is the best known of these flat fish, so we will try to find how its life is spent in the deep sea.

Have you ever watched those little sailing-vessels which go a-shrimping?  They carry a large net—­a shrimp-trawl, it is called—­which is drawn over the sandy home of the Shrimp.  When the trawl is hauled up it may contain not only Shrimps, but the other dwellers in sandy places.  Among these, sad to say, is often a mass of baby Plaice and other flat fish.  Tiny little fellows they are, some hardly as large as a postage stamp.  They are thrown aside, being of no use to the fisherman.

Now these babies are quite flat, darkish on the upper side, white on the other side, like the Plaice you see in the shop.  They are not such new babies after all.  Though such wee mites, it is more than six weeks since they left the egg; and, in that time, they have passed through wonderful changes, as you will see.

Plaice lay a great many eggs, which float about in the sea.  Most are gobbled up by those sea-creatures—­and they are many—­who love fish-eggs for dinner.  From each remaining egg a baby Plaice escapes.  At first it floats upside down at the surface of the sea, and eats nothing at all.  Then it rights itself, and begins to swallow the tiny creatures which swarm in sea-water.

Strange to tell, this baby Plaice is not a bit like its mother.  It is not a flat fish now, but a “round” fish.  It has one eye on each side of its head, and you would expect it to grow up like any other round fish.

For about a month this small, transparent youngster hardly alters.  Then it grows deeper in the body, and begins to swim near the bottom of the sea.  At last it lies on one side, and its life as a “round” fish is over.

A fish lying thus on its side would have one eye buried in the sand, and 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.