CHAPTER VIII 



ADAPTATIONS (CONTINUED)— ADAPTATIONS TO SPECIAL ENDS 



Devices for diminishing weight. Shoulder-girdle and pelvic girdle of tor- 

 toise tribe. Devices in regard to movement and breathing under water. Beaks 

 and teeth in relation to food. Poison-fangs. The chamaeleon's tongue. Blood- 

 squirting from the eyes. Skin-secretions. Spitting. Fluid exudations. Hiss- 

 ing and intimidation. Death-feigning. Immunity to snake-venom. Lungs of 

 chamaeleons and snakes. Voluntary fractures. Rattlesnake's rattle, 



IN the first portion of the preceding chapter attention has 

 been directed to the amount of adaptive variation occurring 

 in the external form of reptiles. Naturally such differences 

 must be correlated with not less imporant differences in the 

 skeleton, and it is some of the more striking of these that now 

 claim attention. During the latter part of the Mesozoic epoch, 

 that is to say, the Upper Jurassic and Cretaceous periods, there 

 existed reptiles which have never been rivalled in the matter of 

 corporeal bulk by any other land animals. Some of the largest of 

 these dinosaurs such as Diplodocus and Brontosaurus (or Apato- 

 saurus) measured about sixty feet in length, and stood something 

 like twenty feet high at the loins, which was the most elevated 

 part of the body. In the case of such monsters it is manifest 

 that if the whole skeleton were solid its weight would be such 

 that either the creature would be unable to move or that the 

 bones would crush one another by their mere dead weight. 

 Obviously the only practicable course was to lighten the skele- 

 ton. To effect this by making the limb-bones hollow would, 

 however, have been out of the question, as bone has not the 

 strength of iron, and hollow columns of the former would have 

 been crushed under the weight of the enormous carcase. On 

 the other hand, it would be feasible to lighten the skeleton by 

 making the vertebral column hollow ; and this has been actually 

 done, the bodies of the vertebrae of these monsters having large 

 cavities on the sides communicating with hollows in the interior. 



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