Smithsonian miscellaneous collections . is well expressed by Tillyard (1917, 1926), Imms (1948), andothers who maintain that the great development of the mesothoracicanepisterna pushes the wings backward away from the head, carry-ing the terga with them, and that the correlated growth of the meta-thoracic epimera pushes the sterna and the legs forward so that thelatter come into position close behind the mouth. However, judgingfrom the courses of the pleural sutures, it is believed that the verticalpositions of the lower portions of the pleural sutures (a condition usu-ally considered to be pr
Smithsonian miscellaneous collections . is well expressed by Tillyard (1917, 1926), Imms (1948), andothers who maintain that the great development of the mesothoracicanepisterna pushes the wings backward away from the head, carry-ing the terga with them, and that the correlated growth of the meta-thoracic epimera pushes the sterna and the legs forward so that thelatter come into position close behind the mouth. However, judgingfrom the courses of the pleural sutures, it is believed that the verticalpositions of the lower portions of the pleural sutures (a condition usu-ally considered to be primitive) probably indicate the primitiveness ofthis region while the posteriorly slanting positions of their upper por-tions probably indicate the evolutionary enlargement of the upperportion of the synthorax. The static nature of the lower region indi-cates that the legs have not been pushed forward, while the poste-riorly slanting position of the upper region indicates that the wings 20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 122. INTERNAL VIEWOF DORSAL PORTION 23 DORSAL VIEW Figs. 21-23.—Synthorax. NO. 6 MORPHOLOGY OF THE DRAGONFLY—CHAO 21 have moved backward away from the head, to a position at or nearthe center of gravity of the greatly elongated body of the insect. Regarding the positions of the three pairs of legs, it is interestingto note that the knee joint between the femur and the tibia of theprothoracic leg is directed sideward, that of the mesothoracic leg, side-ward and backward, that of the metathoracic leg, backward. Thepleurocoxal articulation of the metathoracic leg indicates a rotation ofits axis of about 900. The result of the rotation of the metathoraciclegs might be of definite advantage to the insect in catching prey dur-ing flight or in perching on the twig. The legs are not fitted for walk-ing but they serve very well for climbing when that mode of progressis required. The mesothoracic episternum is divided by an inverted V-shapedsuture into anep
Size: 1346px × 1857px
Photo credit: © The Reading Room / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1860, bookidsmiths, booksubjectscience
