IV. INSECTA: HEXAPODA 



411 



through the spiracles, which are often provided with viljrating membranes 

 which also serve to close these openings. 



The trachete (figs. 437, 452) are usually united, just inside the spiracles, 

 by longitucUnal trunks from which fine 1>ranches extend, enveloping and 

 penetrating all the organs with delicate silvery threads. This connection 

 of trache:e renders it possijjle for the spiracles of some segments to dis- 

 appear, leaving but a single pair in the aquatic larva of some Diptera. 



Fig. 452. Fig. 453. 



Fig. 452. — Anatomy of honey bee (from Lang, after Leuckart). a, antenna^; 

 au, eye; 6, legs; cm^ chyle stomach; ed, rectum; hm, honey stomach (proventriculus) ; 

 rd, rectal glands; st, spiracles; tb, tracheal chambers with trachea;; vm, Malpighian 

 tubules. 



Fig, 453. — Abdomen of Ephemera larva (from Gegenbaur) with tracheal gills, c; u, 

 tracheal trunks; 6, inlcjtin;; d, caudal bristles (cerci). 



The spiracles of the abdomen are the most constant, usually occurring in 

 or near the soft membrane between the sternites and tergites; the thorax 

 at most has but two pairs, the head none. In insects with good powers 

 of flight many of the tracheal trunks are expanded to large air sacs, which 

 may be of value as reservoirs of air, so that the ordinary respiratory 

 motions are less necessary during flight. 



