THE CLASSIFICATION OF ANIMALS 47 



denizens of the earth and air. The few that descend to water 

 take their air-tubes with them, and lead an existence which 

 may be more aptly compared to that of a diver than to that 

 of a purely aquatic animal like a fish. The group Insecta 

 include all the myriad forms of flies, beetles, ants, bees, wasps, 



fw. 



FIG. 19. A beetle viewed from below as an example 

 of Insecta ; at, single pair of antennae ; abd, 

 abdomen; f.w., fore wing ; gri 1 , gn z ,yn*, the three 

 pairs of gnathites; h.w. y hind wing; A, head; J, 

 walking legs ; ih t thorax. 



butterflies, moths, bugs, locusts, grasshoppers, &c. Spiders 

 and mites, although popularly termed insects, really belong 

 to the Arachnida. 



The Crustacea include all our crabs, lobsters, shrimps, cray- 

 fish, and the minnte "water-fleas" which are found in our 

 streams aud ponds, as well as the myriads of similar forms 

 which are fouud in the sea. Speaking broadly, the Crustacea 

 are never harmful to man : some of them, indeed, are directly 



