400 MORPHOLOGY OF THE ABDOMEN IN THE ODONATA 



The Adductor Muscles of the Dorsal Appendage lie latero-dor- 

 sally, and consist of a broad, V-shaped pair, also in the tenth seg- 

 ment. They insert upon the lateral bases of both the dorsal and 

 lateral appendages. 



The small Dorsal Dilators of the Rectum were not clearly made 

 out. There seemed to be suggestions of a pair in the tenth seg- 

 ment. 



Dorso- Ventral and Oblique Segmental Muscles: — • 



The Dorso-Ventral Segmental Muscles (plate XXI, figures 1 

 and 4, dv). In Zygopterous larvae the first nine segments 

 possess a pair each of very thin, delicate vertical muscles laterally 

 placed. The origin of each is upon a- dorso-lateral longitudinal 

 line of the tergite, and the insertion is along a similar Une near 

 the edge of the sternite. The muscle is a little shorter towards the 

 ends of the segment and in some cases there is a tendency to break 

 the band up into separate divisions; this is, however, not constant. 

 It is nearl}'' as wide as the segment is long, and, of course, very 

 short. It seems better developed in Hetaerina and Calopteryx 

 than in Lesies. 



The Dorso-Ventral Oblique Segmental Muscles (plate XXI, 

 figures 1 and 4, dvo). These are present in the first to the ninth 

 segments. Each is a narrow band running from one end of the 

 segment to the other, slanting ventral and caudad. Its origin 

 is upon the anterior tergal suture-fold a little lateral of the mid- 

 dorsum, where it is broadest, and its insertion is upon the suture- 

 fold at the end of the sterno-pleural suture, or partly beneath the 

 end cf the Primary Longitudinal Sternal Muscles. It lies internal 

 to the Vertical Dorso-Ventral Muscle but its upper half is dorsal 

 to the Primary Longitudinal Tergal Muscle, the pressure of 

 which flattens it greatly. 



No traces of Transverse Muscles or Diaphragms were dis- 

 covered. 



II. Anisoptera. Aeshninae 



On account of their large size and the ease with which they can 



be obtained the larvae of Aeschna grandis have served as material 



for most European work on Odonate physiology and anatomy 



during the past half century or more. Dufour's paper of 1852 



