STRUCTURE AND DEVELOPMENT OF INSECTS. 



15 



which chew the leaves, and sucking insects must therefore 

 be killed by other means. 



How Insects Breathe. 



In the side of one thoracic segment and each abdominal 

 segment except the last, of a caterpillar or larva, is a small 



Fig. 7. — Mouth parts of a Plant-louse; a, the jointed beak; b, the 

 lancets, much enlarged; c, antenna; d, foot. (After J. B. 

 Smith. ) 



oval spot, in the centre of which is a slit closed by two 

 membranous lips. These apertures are called sjjiracles or 

 stigmata (Fig. 8, st^-st^^), and are the openings of the 

 respiratory system. Similar openings are to be found in 

 all insects, though not so easily seen in the adults. Con- 

 necting these spiracles is a pair of tubes on each side of 

 the body, throughout its length, from which branch oil' 



