I02 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



spiracles may be of similar structure (caterpillars and other larvae), 

 but usually the closing apparatus of the thoracic spiracles in adult 

 insects effects a movement of one or both of the outer lips of the 

 atrial chamber. 



The Acrididae possess the two usual pairs of thoracic spiracles and 

 eight pairs of abdominal spiracles. The first thoracic spiracle on 

 each side is situated laterally in the ample intersegmental membrane 

 between the prothorax and the mesothorax (fig. 20 B, 26, SP2) where 

 it is covered externally by the lateral part of the large posterior fold 

 of the protergum (fig. 20 B, Rd). The second spiracle lies in the 

 posterior ventral angle of the mesothoracic epimeron just above the 

 base of the middle leg and immediately before the intersegmental 

 groove between the mesopleuron and the metapleuron (fig. 26, Sps). 

 The abdominal spiracles are carried by the first eight abdominal terga, 

 each being placed in the lower anterior angle of the corresponding 

 tergal plate. Tlie first of the series, therefore, lies in the tympanal 

 cavity of the first segment, where it is situated on the small triangular 

 area before the tympanal membrane and just in front of the support 

 of the chordotonal organ. All the spiracles are well developed, and 

 each is provided with an efficient closing apparatus, the mechanism of 

 which presents the usual two types of structure, the first pertaining 

 to the thoracic spiracles, the second to the abdominal spiracles. The 

 details of structure, however, are quite different between the two 

 thoracic spiracles. 



The first thoracic spiracle. — The first spiracle of the thorax of Dis- 

 sostcira Carolina is contained in a small, irregular plate, or peritreme 

 (fig. 51 A, Ptr), lying laterally in the intersegmental membrane 

 between the prothorax and mesothorax (fig. 20 B, SP2), covered 

 externally by the overlapping fold of the protergum. The lower end 

 of the peritreme is produced posteriorly and upward in a small, free 

 process (fig. 51 A, a), bearing on its base a flat-topped, pale-colored 

 tubercle (b) projecting outward. The tubercle is a little higher than 

 the lips of the spiracle and evidently serves as a stop to prevent the 

 covering flap of the protergum from resting too closely against the 

 spiracle. The spiracular opening is an obliquely vertical slit with a 

 slight italic curve and strongly protruding anterior and posterior 

 lips (c, d). The length of the slit is about 0.60 mm. in the male 

 grasshopper, and about 0.75 mm. in the female. The anterior lip (f ) 

 is a rigid elevation of the wall of the peritreme; its inner face is 

 soft and deeply grooved parallel with the outer edge. The posterior 

 lip {d) is a weaker and freely-movable flap, but it has a sharp, 



