78 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



puzzle for insect morphologists until it was shown by Crampton and 

 Hasey (191 5) and by Crampton (1925, 1925a) to be the meron of 

 the middle leg. In the Tipulidse, the plate in question (fig. 34 B, 

 MeVi) is attached to the middle coxa {CX2) and is quite distinct 

 from the postcoxal bridge of the mesothorax {Pcx^). To its upper 

 part is attached the muscle from the subalar plate {So), and to its 

 lower part the tergal remotor of the coxa. The plate is, therefore, 

 the meron, and its relations to the coxa are the same as those of the 

 meron in Panorpa (fig. 34 A), though it forms a part of the seg- 

 mental body wall in the Tipulidse. In the higher Diptera, the corre- 

 sponding plate (fig. 34 C, McTo) is detached from the coxa, and is 

 closely united with a part of the epimeron above it (cpuh), and with 

 the very narrow ]:)OStcoxal bridge (Pcxz) behind it. The body of 

 the coxa (Cxo) is independently movable on a vertical axis. The 

 base of the subalar muscle in the higher Diptera has migrated upward 

 upon the true pleural region, and is attached to the horizontal part 

 of the pleural ridge behind the base of the pleural arm. The remotor 

 muscle of the coxa (fig. 34 D, /), however, remains attached ventrally 

 to the transposed meron (Mcrn) and becomes thus an elevator of 

 the wings, being the middle muscle of the three large wing elevators 

 (C, J, B) in each side of mesothorax. The transposition of the 

 mesothoracic meron in the Diptera from the coxa to the body wall 

 is clearly a device for increasing the power of flight by transferring 

 one of the leg muscles to the service of the wing. 



TJic trochanter. — The trochanter is ordinarily a small segment, 

 usually fixed more or less firmly to the base of the femur (fig. 31 A, 

 7V). Structurally it resembles the coxa, having a strong basicostal 

 ridge (fig. 35 A, g) bearing the coxal articulations, but its motion is 

 limited by the latter to movements in a vertical plane. Being the base 

 of the telopodite, however, its articulation with the coxa is one of 

 the important hinges of the insect leg. The ventral lip of the tro- 

 chanter base usually projects into the coxa as a strong process for the 

 attachment of the extensor muscles (fig. 35 A, P, 0). The 

 trochantero-femoral joint, though usually having but little motion, 

 dififers from all other joints of the insect leg in that, when movable, 

 it bends forward and backward on a vertical axis. A reductor muscle 

 of the femur (fig. 35 A, R) arises in the trochanter and is inserted 

 on a basal thickening (basicosta) of the femur {i). By this character, 

 the true trochantero-femoral suture may be identified where it might 

 otherwise be confused with certain other sutures that sometimes 

 occur near it. 



