280 ELEMENTARY SCIENCE 



The blood of insects does not go through closed vessels, 

 as in man. It fills that part of the body-cavity not occu- 

 pied by other organs. There is a true circulation, however, 

 the heart being located just under the middle of the back. 

 The digestive system is well developed, while there is a 

 central nervous chain that passes along the lower side of 

 the body. 



Of the six great orders of insects, you should understand 

 that two of them have incomplete metamorphosis, while 

 four of them have complete metamorphosis. This long word, 

 metamorphosis, names a very interesting fact of insect Life. 

 You probably know that a caterpillar changes into a moth 

 or butterfly. It is this complete changing from one form 

 into another in the life of an individual that is called 

 metamorphosis. In a complete metamorphosis there are 

 three stages. The egg hatches into a worm-like stage 

 called larva. A caterpillar is a kind of larva. It is in the 

 larval stage that insects do most of then" eating. It is in 

 this stage that they are so harmful to crops and to foliage. 

 Larvae eat almost constantly throughout their lives. After 

 they have stuffed themselves and reached full growth, 

 they pass into a resting-stage, the pupa stage. During 

 this stage they undergo a quite complete change of form. 

 When they emerge from it they usually have wings. They 

 are now in the reproductive or egg-laying stage (see Fig. 

 106). 



Early fall is the best time of year in which to study 

 insects. In early September they are at the height of 

 their activity. You can always find then representatives 

 of the six great orders. 



First, the grasshoppers. They belong to an order called 

 Orthoptera, which means straight wings. Their metamor- 



