ARTHUR DEWITT WHKDOX 399 



to the metathoracie ganglion. They increase in diameter as they 

 pass caudad and insert along the posterior suture of the first 

 sternite, the insertion of the two equaling in width that of the 

 Primary Longitudinal Sternal Muscle of the second segment. 



The Lateral Sternal Thoracico-Abdominal IMuscles (plate 

 XXI, figure 1, Ista). According to Wallengren these compound 

 muscles are inserted on a thin mesothoracic membrane which is 

 stretched over the thoracic ganglia. This membrane is veiy 

 distinct in Lestes and the insertion seems to be directly over the 

 last ganglion. Passing backward and outward the two parts of 

 this muscle increase rapidly in size, and attached to the suture 

 between the thorax and the first abdominal segment near the 

 margin of the sternum ; from this point back to the first segment a 

 broad, bandUke " posterior portion " or extension of these muscles 

 runs to insert upon the posterior suture beneath the Median 

 Sternal Thoracico-Abdominal Muscle. In fact, these "posterior 

 portions" ("hintcre Partien desselben muskels") are quite com- 

 pletely covered by the muscles named. 



Tergal Thoracico-Abdominal Muscles are not develojied. 

 Muscles Controlling the Anal Appendages, Rectum, and other 



appendages : — 



The Ventfal Adductor Muscles of the Lateral Appendages 

 (plate XXI, figure 1, vad). These are intersegmental, with their 

 broad origins at the anterior suture of the ninth segment and their 

 insertions on small, chitinous processes from the inner ventral 

 bases of the lateral appendages. Their shape is that of a narrow 

 V. Just interior to this pair lies another and much more slender 

 pair. 



The Ventral Retractor Muscles of the Anus (plate XXI, figure 

 1, vra) which originate similarly to the above named but unite 

 posteriorly and insert upon the ventral wall of the rectum near 

 the anus. 



A pair of Ventral Dilator Muscles of the Rectum (plate XXI, 

 figure 1, vdrt) may also be discovered as small muscles with 

 their origins contiguous with and dorsal to the Retractors. They 

 run directly back to the rectal wall near the anus. 



The Abtluctor Muscles of the Lateral Appendages (plate XXI, 

 figure 1, ala) lie in the latero-ventral regions of the tenth segment. 

 They are \'-shaped. 



TRANS. .\M. ENT. SOC, XLIV. 



