CHARACTERS OF REPTILES 



CHAPTER VIII 



Reptiles 



THE reptiles are the only vertebrates which are 

 cold-blooded and which without exception 

 breathe by lungs and never at any period of their 

 lives breathe by gills, as do the fishes always and the 

 amphibia for a portion of their lives. They have also 

 invariably a scale-covered skin, in which also there may 

 be supplementary bony structures, such as the bony 

 part of the " box " of the tortoise, and the strong 

 plates in the skin of crocodiles. They possess neither 

 feathers nor hairs. The skull is fixed on to the suc- 

 ceeding vertebral column by one rounded joint or con- 

 dyle as in birds, while the mammals and the amphibia 

 have two of these, one on each side. It is from the 

 amphibia that it is most difficult to divide reptiles, a 

 fact which is embodied in the confusion of the two into 

 one group, called " reptiles " by some of the older 

 authors, and " amphibia " by some others. In past 

 times, as is natural on any theory of evolution, the 

 reptilia and the amphibia gradated into one another, 

 and no very hard and fast line can be drawn. The 

 living representatives of these groups can, however, 

 be distinguished by the characters already enumerated. 

 There are other anatomical characters into the con- 

 sideration of which we shall not enter here. The most 

 obvious character of the reptile is its complete covering 

 of scales. Some extinct groups, such as the Ichthyo- 



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