57 



followed b} 7 an ancient group of reptiles that used to 

 fly. The flying forms among the invertebrates are also 

 illustrated. There are also shown the forms that, 

 like the flying squirrel and flying-fish, are enabled to 

 take advantage of the inertia of the air to take short 

 flights. 



In the back of this case are shown two groups. At 

 the right are nearly all the common domestic animals, 

 as they look in their bones, from the horse to the cat. 

 At the left are a few skeletons of nearly extinct ani- 

 mals, such as the buffalo and wild turkey. 



Modifications of Skin. — The next case illustrates 

 some of the modifications of skin. It should be re- 

 called that the teeth shown in the last case but one 

 are modifications of the skin. Here are shown, be- 

 sides some interesting examples of simple skin, such 

 as that of the elephant and the whale, the latter full 

 of boring shells, the exoskeleton of sponge, star-fish, 

 sea-urchin, crab, insects, shells, etc. Then come such 

 modifications as the hair of mammals, the feathers of 

 birds, the scales of fish and reptiles, the nails, hoofs, 

 claws, and horns of mammals. The bony scales of 

 the alligator, the carapace of turtles, the rattle of the 

 rattlesnake, the beaks of birds and turtles, the quills 

 of the porcupine, etc. 



Eeturning past the west side of the central case, 

 we find several additional illustrations of adap- 



