516 THE OCEAN WOELD. 



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. PLEURONECTID.E. 



The Flat-fishes (Pleuronectidse) have the body flat and greatly 

 compressed, but in a direction different from that of the Eaias and 

 other analogous beings. In the case of the Eaia the body is flattened 

 horizontally, while in the Pleuronectidae 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 

 7T\evpa, side, and z^ro?, swimmers. 



Their chief organ of natation is the caudal fin, but they are distin- 

 guished 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 Plewonectidse, 

 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, 



