NO. 6 GRASSHOPPER ABDOMEN SNODC.RASS 3 



with the primitive sterna in the definitive sternal plates. The lateral 

 tergo-sternal muscles of the ahdomen appear to have no counterparts 

 in the thorax, unless it is to he assumed that they represent the leg 

 muscles that have retained their ventral connections with the coxal 

 elements of the definitive sterna, hut a study of larval insects seems t6 

 indicate that the limb muscles have been lost with the suppression of 

 the appendages. The abdomen of the imago is so completely adapted 

 to its principal mechanical functions of respiration, copulation, and 

 oviposition that the generalized structure in this region of the body 

 is almost entirely obscured by secondary modifications. The acridid 

 abdomen is a good subject for anatomical study, but it throws no light 

 on the general morphology of the insect abdomen. 



CHARACTERISTIC FEATURES OF THE ABDOMEN OF ACRIDOIDEA 



The acridid abdomen consists of ii distinct segments (fig. i). The 

 enlarged first segment is firmly attached to the thorax by its dorsal 



\aiIT IXT XT Eppt 

 \ \ / / Cer 



Papt 



Sg CxCs IS IIS VlllStn 



Fig. I. — Abdomen and base of thorax of Dissostcira Carolina, female. 



and ventral plates (IT, IS), though these plates are widely separated 

 from each other laterally by the hind coxal cavities (C.vCs). On the 

 sides of the first tergum are situated the tympanal organs (Tin) 

 characteristic of the Acrididae, and the first spiracles (ISp) are located 

 in the anterior parts of the tympanal depressions. The following 

 seven segmental annuli (II-VIII) are simple secondary segments 

 separated by ample conjunctivae that allow a considerable extension of 

 the abdomen, as that of the female abdomen during oviposition. The 

 tergal and sternal plates are united by inflected lateral membranes that 

 permit the respiratory movements of vertical expansion and compres- 

 sion. The spiracles of these segments are located in the lower margins 

 of the terga. 



In the female the sternum of the eighth segment (fig. i, V^IIIStn) 

 is the last of the series of ventral segmental plates. It is prolonged 



