INSECTS AND OTHER ANIMALS 3 



The Crustacea (Fig. 1) are mainly water-inhabiting animals which 

 breathe either by gills, or, in the smaller forms, through the surface of 

 the body. In those cases where its members live on land (Fig. 2) the gills 

 are still present, though in a somewhat modified condition. They have 

 numerous pairs of legs and generally two pairs of antennae (jointed 

 "feelers")- Often some of the body segments are fused with the head 

 to form a cephalothorax. 



The Diplopoda (Fig. 3) are land animals breathing by air tubes open- 

 ing on the sides of the body and permitting the air to pass in to all the 

 internal parts of the animal. The head bears a pair of antennas and is 

 followed by a series of segments all practically alike and each, except 



FIG. 4. Centipede (Chilopoda); about three-quarters natural size. (Original.) 



the first three, with two pairs of legs. The reproductive organs open 

 far forward on the body. In most of the more common members of 

 this group the body is quite cylindrical and when disturbed the animal 

 usually curls up in a sort of close spiral. Small Diplopods about the 

 diameter of the lead of a pencil and gray in color are often found boring 

 into potatoes and roots in the ground in the fall, and are sometimes 

 wrongly called wire worms. The common name " millipede" refers to 

 the large number of legs possessed by these animals. 



The Chilopoda are also land animals (Fig. 4). Like the Diplopods 

 they have antennae; breathe by air tubes, and the body segments are 

 practically all alike. The general form, however, is rather flattened; 

 each segment bears only one pair of legs, and the reproductive organs 

 open at the hinder end of the body. The front leg on each side is modi- 



