ENTOMOLOGY 



regular opening and closing movements of some of the spira- 

 cles and the rhythmic contraction and expansion of the abdo- 

 men. During contraction, the dorsal and ventral walls ap- 



Tracheal capillary end-network from silk gland of Porthetria dispar. p, peritracheal 

 membrane; t, tracheal capillary. After WISTINGHAUSEN. 



proach each other (Fig. 176) and during expansion they 

 separate. The tergum moves more than the sternum in Cole- 

 optera and Heteroptera, and vice versa in Acridiidae, Odonata, 

 Diptera and aculeate Hymenoptera. The width of the abdo- 

 men usually changes but little during respiration, for the ter- 

 gal and sternal movements are taken up by the pleural mem- 



FIG. 176. 



Transverse sections of abdominal segments, to illustrate respiratory movements. A, 

 cockroach (Blatta) ; B, bee (Bombus) ; s, sternum; t, tergum. The dotted lines 

 indicate positions of terga and sterna after expiration; the continuous lines, after 

 inspiration. After PLATEAU. 



branes which, as in the grasshopper, infold at contraction and 

 straighten out at expansion. Other respiratory movements 

 occur, but they are of minor importance. 



