Smithsonian miscellaneous collections . tum with the dorsal and pleural sclerotic partsof the metathorax, the lobes of the third phragma are securely bracedagainst the pull of the dorsal muscles attached on them (fig. 3 A). Theforce of the muscles, therefore, is expended on the alinotum of themetathorax (AN3), which responds by an upward curvature that de-presses the wings on the pleural fulcra. In the usual intersegmentalmechanism of secondary segmentation, in which the acrotergite is amere flange on the anterior margin of the tergum following, and isseparated by a conjunctival membrane from
Smithsonian miscellaneous collections . tum with the dorsal and pleural sclerotic partsof the metathorax, the lobes of the third phragma are securely bracedagainst the pull of the dorsal muscles attached on them (fig. 3 A). Theforce of the muscles, therefore, is expended on the alinotum of themetathorax (AN3), which responds by an upward curvature that de-presses the wings on the pleural fulcra. In the usual intersegmentalmechanism of secondary segmentation, in which the acrotergite is amere flange on the anterior margin of the tergum following, and isseparated by a conjunctival membrane from the preceding tergum, thecontraction of the longitudinal muscles produces an approximationor overlapping of the consecutive segmental plates. The enlargement NO. 6 GRASSHOPPER ABDOMEN SNODGRASS of the acrotergite of the first abdominal tergum, accompanied by anobliteration of the conjunctiva behind the wing-bearing plate of themetathorax, is clearly, therefore, a device to suppress intertergal move-ment at this intersegmental Papt Fig. 4.—Dorsal view of the inner surface of the skeletal plates of the meta-thorax and abdomen of Dissosteira Carolina, female; ovipositor removed ex-posing the floor of the genital chamber, the gonopore (Gpr), and egg guide (eg). The ventral union of the abdomen with the thorax in Acrididae iseven more complete than is the dorsal union. The sternum of the firstabdominal segment (fig. 2 B, IS) forms virtually a part of the ptero-thoracic plastron. Its acrosternite is either a broad lobe (fig. 4, ost),or a narrow tongue (fig. 2 B, ast), but in either case it is solidly fused 10 SMITHSONIAN MISCELLANEOUS COLLECTIONS \0L. 94 with the metasternum in the notch between the sternellar lobes (SI3).There are no ventral muscles that extend from the thorax into theabdomen in Acrididae, and the first ventral muscles of the abdomentake their origin on a transverse ridge of the first abdominal sternumat the base of the acrosternite (fig. 8, 143). This
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Keywords: ., bookauthorsm, bookcentury1800, bookdecade1860, booksubjectscience
