CHAPTER XII 



THE FLAT-FISHES 



With the exception of the dory and one or two of the rarer 

 riband-like fishes inhabiting deep water, all the bony fishes 

 hitherto considered exhibited a roundness of form, swam in 

 the upright position, and had perfect symmetry on both sides, 

 even to the smallest blotch or marking. In the rays, it is true, 

 we found flattened fishes, but there was no want of similarity 

 in the sides, for the apparent upper and lower surface of the 

 ray is the actual back and belly of the fish, and the ray is 

 therefore merely a compressed, or depressed, shark peculiarly 

 adapted for residence at the bottom of the sea. That the 

 upper surface should be coloured and the lower surface white 

 is, therefore, only the same condition as we find in the upper 

 and lower surface of the cod, mackerel, or gurnard. In the 

 flat-fishes, however — the plaice and sole and turbot — we have a 

 totally diff^erent condition. Here, what appears to be the back 

 and belly of the fish is in reality the right and left side. The 

 actual back .and belly of the flat-fishes are the finny edges, 

 which have become compressed out of all resemblance to the 

 normal condition. Why, or when, the flat-fishes, as they are 

 now known to us, developed this extraordinary shape and 

 position, we cannot tell. They are not so when hatched from 

 the egg, so that their ancestors in all probability swam as 

 other fishes. But during the first few weeks of their existence 

 they gradually lean over on one side (the left in most cases), 

 which is henceforth pressed close to the sand and withdrawn 



