Human Physiology. 



129 



cases to those displayed by insects. The rattlesnake is a 



remarkable instance. In his head is a gland which secretes a 



deadly venom, a bladder to hold it, a tube to carry it to a long 



curved, hollow, sharp fang, 



which is commonly folded out 



of the way, but which can be 



brought down at will. When 



an angry bite is inflicted, the 



venom is pressed through the 



tooth. This venom kills if it 



enters the circulation, but may 



Fig. 6. 



be swallowed with impunity. But it is a gentle snake, and 

 always gives warning before it strikes. To enable it to do 

 this it has a rattle at the end of its tail, several joints t . 

 of dried bone, which rattle together and give the 

 intruder fair notice. 



This world would be much less interesting and 

 delightful than it is without the birds, who charm 

 us with the beauty of their forms and plumage, and 

 the sweetness of their songs. A world that has in 

 it skylarks, mocking-birds, and nightingales is not so 

 bad. 



As mechanism, nothing could be nicer light, 

 strong skeletons, as well shaped for flying as a fish 

 for swimming; muscles massed just where they are wanted; 

 feathers, each a marvel of a light, strong, beautiful covering; 

 broad, spreading wings made for the air, as the air for them ; 

 legs with tendons bending the toes with the weight of the bird, 

 so that it can sleep on its perch securely. 



Little brains, but how wise ! It needs no lessons to build its 

 nest, and the first bird built as well as the bird of to-day. Some 

 burrow in banks of earth, some hang their nests from boughs 

 of trew*- The tailor bird sews up a leaf for his nest. They 

 know when to migrate, where to go to in winter, and find their 



T 



Fig. 7. 



