Fig. 369. Echineis remora.
The Echineis remora is an inhabitant of the Mediterranean, and abounds in the Indian and Atlantic Oceans. It is furnished with a flat disk, which covers its head, as represented in Fig. 369, which is formed of a number of transverse and movable cartilaginous plates. Aided by this organ, it attaches itself firmly to rocks, and even to ships and larger fishes, such as the Dog-fish (Acanthius), which it meets with in its wanderings. Its adhesion to those objects is so strong that the strength of a man fails to separate them. It invariably attaches itself to the dorsum and flank of the shark, and sometimes weighs a pound and a quarter. "I have found," writes a friend, "as many as seven on one shark." It is never solitary, and makes long voyages on this monstrous animal locomotive, and that without fatigue or danger, for its enemies are kept at a distance by the formidable monster which carries it.
II. PLEURONECTIDÆ.
The Flat-fishes (Pleuronectidæ) have the body flat and greatly compressed, but in a direction different from that of the Raias and other analogous beings. In the case of the Raia the body is flattened horizontally, while in the Pleuronectidæ they are compressed laterally. The head of fishes of this order is not symmetrical; the two eyes are placed on the same side; the two sides of the mouth are unequal.
To these peculiarities of structure we shall return when we come to observe the several types more clearly. In inaction, as in motion, the flat-fishes are always turned upon their side, and the side turned towards the bottom of the sea is that which has no eye. This habit of swimming on their side is that to which they owe their name of πλευρὰ, side, and νέχτος, swimmers.
Their chief organ of natation is the caudal fin, but they are distinguished from all other fishes by the manner in which they use this oar. When turned upon their side this organ is not horizontal, but vertical, and strikes the water vertically up and down. They advance through the water but very slowly, compared to the motion of other fishes. They ascend or descend in the water with greater promptitude, but they cannot turn to the right or left with the same facility as other fishes. This property of rising or sinking in the water with facility is the more useful to them, inasmuch as the greater part of their existence is passed at the greatest depths, where they draw themselves along the sands at the bottom of the sea, and often hide themselves from their enemies. Among the Pleuronectidæ, soles, turbot, flounders, and plaice may be noted.
Soles (Solea) have the body oblong, the side opposite to the edges generally furnished with shaggy, soft hairs; the muzzles round, nearly always in advance of the mouth, which is twisted to the left side, and furnished with teeth on one side only, while the eyes are on the right side. The dorsal fin commences about the mouth, and extends up to the caudal or terminal fin. The Common Sole, Solea vulgaris (Fig. 370), is plentiful in the Channel, along the Atlantic coasts, and especially in the Mediterranean. It is brown on the right, and whitish on the opposite side. Its pectoral fins are spotted black; the scales rugged and denticulate; its size seems to vary according to the coast it frequents. Off the mouth of the Seine soles are sometimes taken eighteen and twenty inches in length. There are several modes of taking them, but for commercial purposes it is taken by the trawl-net. When the ground-hook is employed it is baited with fragments of small fish. Every one knows the delicate flavour of the flesh of the sole, which, however, varies greatly in different localities, those of the Channel Islands being particularly choice.
Fig. 370. The Common Sole (Solea vulgaris).
The Turbot, Rhombus maximus (Fig. 371), resembles in its general form a lozenge, whence its name of rhombus. Its under jaw is more advanced than the upper jaw, and is furnished with many rows of small teeth. Its fins are yellow, with brownish spots. The left side is marbled brown and yellow; the right side, which is the inferior, white with brownish spots and points. The true turbot is the special delight of the epicure, and fabulous sums are said to have been given at different times by rich persons in order to secure a fine turbot. The fish used to be taken largely on our own coasts, but now we have to rely upon more distant fishing-grounds for a large portion of our supply—large quantities coming from Holland. The turbot spawns during the autumn, and is in fine condition during spring and early summer. Mr. Yarrell says that it spawns in spring. Dr. Bertram doubts this, although he is not quite sure of it, inasmuch as "there will, no doubt, be individuals of the turbot kind, as there are of all other kinds of fish, that will spawn all the year round." The turbot abounds on our west coast, round Torbay, and off the mouth of the Seine and the Somme, from whence comes most of the fish consumed in London and Paris. The flounders, plaice, and halibut form an important section of the Pleuronectidæ.