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EVOLUTION OF ANIMALS 



Part V 



Fig. 33.8. The streamlined bodies of fishes and the variations that are usually 

 associated with a reduction in the efficiency of swimming and the development 

 of some protective mechanism. A, mackerel, a streamlined fish known to travel 

 more than twenty miles an hour. B, trunk fish (Ostracion) whose scales form a 

 rigid box; it lives in coral pools browsing on the polyps. C, sunfish (Mola), may 

 have a length of 5 feet or more and, whatever the advantages may be, has 

 managed to inhabit all temperate and warm oceans. D, globe fish (Chilomycterus) 

 is slow moving but has heavy armor. E, sea horse (Hippocampus) has no caudal 

 fin but anchors itself by its prehensile tail. F, common eel (Anguilla) that can 

 squirm over barriers between bodies of water. (Courtesy, Young: The Life of the 

 Vertebrates. Oxford, England, The Clarendon Press, 1950.) 



of dead cells and like them have a growing part or quick. In most fishes, the 

 scales are covered by a layer of skin, so thin it is invisible, and usually worn 

 off at their tips. In others such as in the various species of trout, they appear 

 only when the surface of the body is rubbed lightly; in eels, they are deeply 

 hidden and it is commonly thought that there are none. In bony fishes, the 

 scales overlap one another like shingles. The visible part of each one is 

 smaller than the hidden part and always points away from the head. In black 

 bass and others, the scales are ctenoicl, i.e., comblike with toothed edges; in 



