28 THE STORY OF FISH LIFE. 



fashion, a new improvement was introduced 

 the air-bladder. This in turn can be fol- 

 lowed through a series of transformations which 

 gradually change it into a lung, and so more or 

 less completely do away with the need of gills 

 at all. If we had the time we could go further 

 still, and follow these lungs into still greater 

 stages of perfection ; but this must be left for 

 another day. 



CHAPTEE III. 



HOW FISH ARE CLOTHED. 



SOME fish, such as the lampreys, many eels, and 

 all fishes provided with well-developed electric 

 organs, have the skin entirely naked. These are, 

 however, exceptions, and there is good reason to 

 believe that this nakedness is, at least in most 

 cases, a degenerate character. That is to say, 

 scales were once present, but have now dis, 

 appeared. Thus, in many eels, if the skin be care- 

 fully (microscopically) examined, minute scales 

 will be found embedded therein. These, we infer, 

 are remnants of once much larger structures, 

 which served, at the heyday of their develop- 

 ment, to completely invest the body. 



The typical scaly clothing of a fish may perhaps 

 best be studied in a roach or perch. In such a 

 fish we should notice that the whole body, save 

 the head and fins, was covered by a series of 

 horny plates overlapping one another like the 

 tiles on a roof. If we removed one of these 



