266 



A YEAR IN SCIENCE 



Insects breathe by means of air tubes which are con- 

 nected with the outside through openings in the sides of 

 the body. 



Many of the insects undergo complete changes, or 

 metamorphoses, when they develop. For example, the 

 egg of the monarch or milkweed butterfly is laid in 

 late spring. In a few days it hatches into a worm-like 

 larva called a caterpillar. The caterpillar grows very 



Fig-. 123. Development of the sphinx moth; L, larva; C, chrysalis; 



A, adult. 



rapidly for a few weeks. Then it stops eating and 

 begins to spin a mat of silk upon a leaf or stem. It 

 attaches itself to this web by the front legs and hangs 

 there. After about twenty-four hours it has passed 

 into a resting stage and is called a pupa, or chrysalis. 

 After a week or more of inactivity, the shell splits and 



