160 VERTEBRATA. PISCES. 



family before us, consisting of the Flat-fish, as they 

 are familiarly called, this symmetry no longer exists. 

 They swim not in an upright position, but upon one 

 side, as if we should imagine a Salmon to swim in 

 the position in which it lies on the fishmonger's 

 table. Some species have the right side, and some 

 the left uppermost ; but it is always normally the same 

 side in the same species. Now, as they are ground- 

 fish, always keeping at the bottom, if the eyes were 

 placed as usual, one would be useless, being im- 

 mersed in the mud ; they are therefore, strange to 

 say, both placed on one side, one being immedi- 

 ately above the other, not always, however, exactly 

 in a line, nor are they always equal in size. Again, 

 the upper side monopolizes all the colour of the fish 

 which is usually of a dark brown, the under side 

 being white. It is easy to see the wisdom of this 

 arrangement. The two sides of the mouth are not 

 equal, nor are, generally, the pectoral fins. Yet, 

 with all these irregularities, the skeleton is found 

 to be constructed on the common plan, all the usual 

 bones being present, however modified in figure and 

 situation. We may add, to the peculiarities al- 

 ready mentioned, a few other distinctive characters ; 

 the whole form is extremely thin and flat side wise, 

 but broad and more or less lozenge-shaped in its 

 outline ; the dorsal runs along the whole back, and 

 the anal along the belly, so that the latter with the 

 ventrals almost exactly answers to the former : the 

 gills have six rays. 



Being destitute of the air-bladder, Flat-fishes are 



