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are attached respectively to a kind of shoulder- 

 bone and hip-bone ; and they are all moved by 

 very strong muscles, which take a lamellar struc- 

 ture, but are still in general colourless those, 

 however, about the head of the salmon are of a 

 red colour, and all those of the lamprey of a dark 

 grey. Some tribes effect their progression by 

 the motions, not of a fin, but of the spine for 

 example, the lamprey which has neither pecto- 

 ral nor ventral fins, and which seems to move in 

 its natural element, the mud, entirely by the la- 

 teral flexion of its spine, which it at first draws in- 

 to an S-like curve, and then shoots forwards the 

 anterior portion. The same is th6 case, also, 

 with the eel, when it creeps on land. Others 

 again, as most of the flat fishes, which, like the 

 lamprey, have neither pectoral nor ventral fins, 

 use their tails principally in making progress in 

 the water. The bodies of fishes are of very 

 nearly the same specific gravity as the water in 

 which they live, owing to the great quantity of 

 fat which most of them contain ; so that little 

 effort is required to keep them at any given 

 height, and their descent or ascent in the water 

 is comparatively easy, the latter being further 

 promoted by the faculty they possess, and to 

 which I have elsewhere alluded, of filling their 

 air-bladder at pleasure with air. When they at- 

 tach themselves to rocks, it is by means of suck- 

 ers like those of the cuttle ; and when they leap 

 from the surface of the water, it is by the sudden 

 and forcible extension of their bodies after a strong 



