ARTHUR DEW'ITT WHEDOX 417 



segment and has dorsal, lateral, and ventral aspects, its muscles 

 are largest and produce most of the movements. 



The Superior Longitudinal Tergal Muscles (figures as above) 

 are short band-like or fan-shaped muscles in pairs, one member 

 on each side of the mid-dorsal line. In Caloptenjx they are 

 slightly separated; in Megaloprepus they interlock. The origin 

 is upon the face of the tergum near its posterior end, the insertion 

 upon the extreme anterior dorsum of the succeeding segment. 

 They are wide enough to reach far ventrad on the sides of the 

 tergum, almost or quite touching the Inferior Longitudinal 

 Tergals. 



The Inferior Longitudinal Tergal Muscles (plate XXV, figures 

 17, 21, and 23) are nearly twice as long as the superiors and are 

 much thicker. They have a broad region of origin over the lateral 

 and ventral portion of the tergite, becoming narrower at their 

 insertion on the anterior corners of the tergum of the succeeding 

 segment at the pleuro-tergal suture. 



The Inferior Longitudinal Tergo-pleural Muscles. In the 

 forms of Zygoptera dissected these muscles are not very distinct 

 from the last named. They have the same origin but a different 

 insertion, and are plainly separable in the second segment of 

 female Zygoptera, and in all segments of the Aeshninae. It is 

 probable that they have arisen by the migration of the point of 

 insertion away from the tergum and toward the pleural region 

 nearest the sternum ; this places them beneath the anterior sternal 

 process. It is conceivable, of course, that the evolution has been 

 in the opposite direction, thus deriving the apparently single 

 muscle of the most of the segments from the two. However, the 

 presence of two muscles in the Aeshninae would point in the other 

 direction. They are thin and weak and in the Libellulinae they 

 are not present. 



Longitudinal Thoracico- Abdominal Muscles: — 



The Submedian Ventral Thoracico-Abdominal Muscles (plate 

 XXV, figures 17 and 23, svta; plate XXVII, figures 31 and 30). 

 A pair of very strong muscle bands which develop from, or replace, 

 the sternals of the first segment. They attach to the abdomen 

 on the anterior corners of the sternite of the second segment and 

 to the thorax by a common tendon, the posterior epimeral apo- 

 <ieme. 



TRANS. AM. ENT. SOC, XLIV. 



