54 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



ventral region (PV). The sclerotic thickenings form attachment 

 points for muscles on the inner abdominal wall (B). 



The musculature of the visceral segments in the abdomen of Gryllus 

 comprises the usual dorsal, ventral, lateral, transverse, and spiracular 

 muscles. The following muscles may be distinguished in an individual 

 segment, such as the fifth or sixth, shown at B of Figure 15. 



The dorsal muscles consist of two sets of longitudinal fibers, both 

 of which apparently belong to the internal system, since no muscles 



u 



Fig. 15. — Relation of the musculature to the integumental areas in the abdomen 

 of Gryllus asshnilis. 



A, lateral and ventral parts of two consecutive segments, with separation be- 

 tween dorsum (D) and pleuroventral region (PV) indicated by dorso-pleural 

 line (_a-a). 



B, musculature of right half of segments V and P/. 



a-a, dorso-pleural line; D, dorsum; Id, laterodorsal area; P, pleural region; 

 pi, series of pleurites ; pt, series of paratergal sclerotizations ; PV, pleuroventral 

 region; Stn, sterna; T, terga. 



lie external to them. The fibers of one set, the median dorsals (dim), 

 form in each segment a narrow band of segmental length on each side 

 of the median line of the back, attached to the anterior margins of 

 successive terga. The fibers of the other set, the lateral internal dorsals 

 (dil), occupy the wide lateral parts of the terga, but they are confined 

 to the posterior parts of the segments, since they arise behind the mid- 

 dle of the tergal plate before the one on which they are inserted. 



The ventral longitudinal muscles comprise internal ventrals (vi) 

 of segmental length located laterally on the sterna, and external ven- 



