IV. INSECTA: HEXAPODA 



411 



through the spiracles, which are often provided with vibrating membranes 

 which also serve to close these openings. 



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

 by longitudinal trunks from which fine branches extend, enveloping and 

 penetrating all the organs with delicate silvery threads. This connection 

 of trachea renders it possible for the spiracles of some segments to dis- 

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



Jr 10 



nut 



cm 



ed. 



FIG. 452. FIG. 453- 



FIG 4-52. Anatomy of honey bee (from Lang, after Leuckart). a, antennae; 

 au eve; b, legs; cm, chyle stomach; ed, rectum; km, honey stomach (proventaculus) 

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



tubules. 



FIG. 453. Abdomen of Ephemera larva (from Gegenbaur) with tracheal | 

 tracheal trunks; b, intestine; 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 tergitrs; tin- thorax 

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

 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. 



