CLASS PISCES. 491 



Pleuronectes ', L. 



They have a character which is unique among 

 vertebrated animals, that is the want of symmetry in 

 the head ; both eyes being on the same side, which 

 remains uppermost when the animal swims, and is 

 always strongly coloured, while the side in which the 

 eyes are wanting is invariably whitish. The rest of 

 the body, though in general disposed in the ordinary 

 way, participates a little in this irregularity ; thus the 

 two sides of the mouth are not equal, and it is but 

 seldom that the two pectorals are so. Their body is 

 very much compressed, and elevated vertically. The 

 dorsal runs along the whole of the back ; the anal 

 occupies the under part of the body ; and the ven- 

 trals have almost the appearance of continuing it for- 

 ward, inasmuch as they are often united one to the 

 other. There are six rays to the gills. The abdo- 

 minal cavity is small, but is prolonged into a sinus, in 

 the thickness of the two sides of the tail, to lodge 

 some portion of the viscera. There is no natatory 

 bladder; and these fishes seldom quit the bottom. 

 The skeleton of their cranium is curious, in conse- 

 quence of this inversion, which brings the two orbits 

 on one and the same side. Nevertheless, we find in 



1 Pleuronectes, is a name composed by Artecli, from irXevpci, the 

 side, and rv^rtjc, a swimmer ; because they swim upon the side. The 

 ancients gave them different names, according to the species, such as 

 Passer, Rhombus, Biigfossa, &c. 



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