Fig. 12.
The Common Sole.[48]
Above are two small soles as they swim when young. At that time they are not larger than a grain of rice.—(Adapted from Figuier and Malm.)
If we wanted to pick out the strangest and strongest proof of how the shape of fish is altered to suit their wants, we need seek no further than the flat-fish.
When we were speaking of the shark order we saw that the rays and skates are flattened forms suited to hide in the sand, and these fish are truly spread out as if they had been squeezed under a heavy weight, their broad arm-fins edging the sides of their body. But the bony flat-fish, the Soles and Turbot, have a far stranger history. The young sole, when it comes out of the egg, is not flat like the young skate, but a very thin spindle-shaped fish, something like a minnow. He is then about the size of a grain of rice, very transparent, and lives at the top of the sea. He has one eye on each side, like other fish, only one eye is higher up than the other, and the single fin on its back and the one under its body reach almost from head to tail. In this way he swims for about a week, but he is so thin and deep, and his fins are so small, that swimming edgeways is an effort, and soon he falls down on one side, generally the left, to the bottom of the sea. Many times he rises up again, especially at first, till he has got used to breathing at the muddy bottom, and meanwhile the eye that lies underneath is gradually working its way round to the upper side, his forehead wrinkles so as to draw the under eye up, while his whole head and mouth receive a twist which he never afterwards loses. His skeleton, it must be remembered, is still very soft, and the bones of his face are easily bent; and at last this eye is screwed round, and as he lies at the bottom he can look upwards with both eyes and save the under one from getting scratched by the sand, as it must have done if it had remained below.
Nor is this all, for while his under side, shaded from the sunlight, remains white and colourless, his upper side gradually becomes coloured like the sand in which he lies, and he is safely hidden from attack as he flaps along, feeding on worms and other animals. And now when he swims he no longer uses his arm and leg fins, which are quite small and insignificant, but bends his whole body, using the back and belly fins to help him. What we then call the top of the sole is really his side, where you may see the dark line of scales running along the middle, and one arm-fin lying close to his head. Yet he can swim strongly and to far distances, for in the winter the soles, too, migrate into the open sea, where they may be found in the deep water of the Silver Pit, between the Dogger Bank and the Well Bank.
Fig. 13.
Hippocampus, a fish commonly called the Sea-Horse.