INSECTS 



27 



b. Will the air tubes be made larger or smaller? 



Why? 



c. Will the air now rush into the air tubes or out of 



them? Why? 

 If the upper and lower halves of the abdomen now 



move apart — 

 Will the diameter of the abdomen be increased or 



decreased ? 

 How will this movement affect the size of the 



tracheae? Why? 

 Will the air now move into the tracheae or out 



through the spiracles? Why? 



a. 



b. 



21. Characteristics .of grasshoppers. — After studying 

 two or three insects, the student will see that they all re- 

 semble the grasshopper (1) in having three regions of the 

 body (head, thorax/ and abdomen), (2) in possessing as 

 appendages one pair of antennae, one pair of compound eyes, 

 two pairs of wings, and three pairs of legs, and (3) in having 

 an abdomen made up of a number of rings or segments. 

 The most distinguishing character- 

 istics of the grasshopper and its rela- 

 tives are found in its mouth parts 

 and wings. Grasshoppers have bit- 

 ing mouth parts throughout their 

 life. These consist of (1) an upper 

 lip that is notched, (2) a pair of 

 horny jaws, or mandibles, (3) a pair 

 of rather compUcated helping jaws or 

 maxilla, and (4) a lower lip. The two 

 lips move up and down while the two 

 pairs of jaws move from side to side. 

 All these structures are well adapted 



for holding and biting off leaves of grass or other plants 

 and this seems to be the main business of this insect. 



Fig. 18. ^ Mouth parts of 

 a cockroa'ch. (Parker 

 and Haswell.) 



