NO. 6 GRASSHOPPER ABDOMEN SNODCRASS 7 



lobes (Ap) projecting forward from the anterior margin of the tergum 

 for muscle attachments. 



The abdominal sterna of the Acrididae reseml)le the terga in that 

 each is an undivided plate, but the sterna, as with pterygote insects 

 generally, are presumably coxosternal plates in composition, though 

 there are no styli on any of the abdominal segments. The first ab- 

 dominal sternum (fig. 4, IS) is closely united with the metasternum 

 of the thorax by an anterior extension (ast), which appears to be 

 the acrosternite ; otherwise it is a simple plate. The following sterna 

 have each a pair of large apodemes on their anterior angles. The 

 apodemes of the second and eighth sterna in the female (fig. 4), 

 or of the second and ninth in the male (fig. 12), are simple anterior 

 arms ; but the intervening apodemes have lateral expansions that 

 form distinct lateral apodemes in the more anterior segments of 

 the female (fig. 4, lAp) and in all the segments of the male be- 

 tween the second segment and the ninth (fig. 12). The lateral 

 apodemes give attachment to the dilator muscles of the abdomen (fig. 

 10 B, lie), which have their dorsal attachments ventrally on the lower 

 edges of the terga. The intersegmental ventral muscles of the abdomen 

 have their anterior attachments on the sterna some distance back of 

 the anterior margins of the latter (figs. 8, 10 A) , but they are attached 

 posteriorly on the anterior margins of the sterna following. In the 

 male the lines of origin of these muscles are strengthened in each 

 segment by a well-developed transverse sternal ridge (fig. 12, sr) ; 

 in the female the ridges are present only on the sterna of the more 

 anterior segments (fig. 4). The musculature of the abdomen, and 

 cuticular developments related to the muscles are in general weaker 

 in the female than in the male. 



In the Tetrigidae the median sternal plates of the abdomen appear 

 to correspond with the sternal plates of Acrididae since they bear the 

 sternal apodemes on their anterior angles. The small laterosternites 

 (fig. 2 C, D, 1st), therefore, are probably secondary developments in 

 the membranes laterad of the sterna, and in a loose sense may be 

 termed " pleurites," though there is nothing to suggest that they repre- 

 sent remnants of limb bases. According to Ford (1923) there are 

 no muscles attached on the laterosternites of Tetrigidae, but there are 

 groups of small lateral muscles attached dorsally in the membrane be- 

 fore and behind the spiracles and ventrally on the sterna. These mus- 

 cles are evidently dorsosternal muscles, since the region of the spir- 

 acles is to be regarded as a part of the dorsum. The principal lateral 

 muscles in Tetrigidae, as in Acrididae, are tergosternal muscles. 



