222 ELEMENTS OF COMPARATIVE ZOOLOGY. 



with them in their search for food. These caddis-flies, in 

 the adult stage, have the mouth-parts much reduced, and 



FIG. 99. Adult ant-lion (Myrmeleon). 



are supposed to represent pretty closely the ancestors of the 

 butterflies and moths (Lepidoptera). 



ORDER V. COLEOPTERA (see p. 184). 



ORDER VI. HYME^OPTERA (seep. 188). 



ORDER VII. HEMIPTERA (see p. 194). 



ORDER VIII. LEPIDOPTERA (see p. 199). 



ORDER IX. DIPTERA (Flies). 



This order contains the true flies, and these forms are 

 sharply marked off from other insects. The name means 

 two- wings, and the flies have but a single pair of these 

 organs, while on the metathorax is a pair of knobbed hairs, 

 the so-called balancers. The mouth-parts are fitted for 

 sucking. The larvae, commonly known as maggots, are 

 worm-like, lack feet, and in some species even lack a dis- 

 tinct head. In some the pupa is motionless, but in others, 

 as in the mosquito, it has great powers of motion. The 

 balancers are sensory organs, and they also serve as a 

 means of maintaining the equilibrium, for if they be cut off 

 from a fly, the animal can no longer direct its motions. 



The group of flies is very large in number of species, 

 some being beneficial, while others are decided pests. 

 Among the latter are those forms which feed upon other 



