124 STORY OF THE REPTILES 



ried into the system, thereby imparting energy and 

 strength to the various parts of the body. It is no 

 use to eat unless you can breathe, and no use to 

 breathe unless the blood can circulate. Hence the 

 grouping of these topics. Reptiles, as noted, breathe 

 by lungs mostly, never by gills. To some extent the 

 aquatic turtles breathe by the skii), though there is 

 no such arrangement for this in these as there is in 

 the amphibians. There are, however, near the skin 

 some places where arteries are massed and twisted or 

 meshed together, evidently to store aerated blood for 

 use under water, if not for getting it further oxi- 

 dized through the pores. This is the case, perhaps, 

 in water-haunting tortoise-forms only. 



Lungs 



The lungs in the average reptile are better than 

 those of the average apaphibian, but in many cases 

 they still show a tendency to be mere sacs or pockets 

 at the rear ends. With such imperfect lungs and a, 

 heart three-chambered only, we should still expect 

 cold blood, as is the case in all living reptiles. In the 

 old, very active Dwwsaurs (of which more later) the 

 bones were hollow and connected with the lungs ; and 

 there were, perhaps, other air sacs among the muscles, 

 to help a small poor lung out in unusual work. 



There can be no doubt that bones in birds and 

 other creatures are made hollow to make them light 

 and yet strong ; but the air does not enter them to 

 make them buoyant — ^Qotwithstanding that yon will 

 see such a statement made over and over even by fair 



