64 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



clature of these writers has not been generally adopted. Lendenfeld 

 details the wing structure and all parts concerned with the wing 

 action in the Odonata ; Amans gives a comprehensive comparative 

 study of the wing mechanism in the principal orders of insects. 

 Following these papers, accounts of the structure, musculature, and 

 mechanics of the wings of various insects are contained in the works 

 of Luks (1883), Janet (1899), Petri (1899), Voss (1905, 1912), 

 Diirken (1907), Berlese (1909), Snodgrass (1909), Bauer (1910), 

 Groschel (1911), Stellwaag (1910, 1914), Crampton (1914), 

 DuPorte (1920), Weber (1924, 1925), The nature of the wing 

 movements in insects has been studied particularly by Marey (1869, 

 1869/72), Lendenfeld (1903), Stellwaag (1910, 1914), and Voss 



(1913/14)- 



The wing of most insects has four cardinal movements : elevation, 

 depression, Hexion, extension. In addition, the wing is capable of a 

 slight rotation on its long axis. Elevation and depression are vertical 

 movements efifected primarily by the longitudinal and oblique tergal 

 muscles, and the tergo-sternal muscles of the thorax, but the coxal 

 muscle of the epimeron becomes a strong accessory depressor of the 

 wing in the adult. The flexor of the wing is the muscle of the third 

 axillary sclerite of the wing base ; the extensors are chiefly the mus- 

 cles of the basalar and subalar sclerites. The partial rotary movement 

 of the wings may be a mechanical result of the wing structure and 

 of the reaction of the wing surfaces to pressure of the air during 

 flight, but probably it is controlled by the epipleural muscles. 



The tergal and tergo-sternal muscles of the thorax that principally 

 efifect the elevation and depression of the wings are known as the 

 indirect zving muscles, because they produce wing movements through 

 causing alternating changes in the shape of the thorax. The depres- 

 sors consist of the pair of great dorsal longitudinal muscles, typically 

 stretched between the phragmata (fig. 28, A), but often so. large that 

 they encroach a varying distance upon the anterior part of the scutum 

 (fig. 29, A, A). The oblique dorsals, extending laterally from the 

 posterior part of the scutum to the posterior phragma (fig. 28, B), 

 are proliably accessory to the longitudinals in some cases. l)ut in others 

 their positions become so nearly perpendicular to the tergum (figs. 29. 

 34 D, 5) that they must act as elevators of the wings. These mus- 

 cles are of extraordinary size in the cicada (fig. 29, B). The usual 

 elevators of the wings include always the pair of large vertical mus- 

 cles in the anterior part of the thorax (figs. 28, 29, C), attached 

 dorsally to the scutum laterad of the longitudinals, and ventrally to 



