ARTHUR DEWITT WHEDON 411 



longitudinal muscles of both sternum and terguin resemble Lestes; 

 the dorso-ventral muscles are more like those of Anax and Aeshna. 

 The appendages are controlled by a similar mechanism in all 

 groups. 



Segmental Muscles of the Sternum: (Plate XXIV, figures 13 

 and 15) — 



The Primary Longitudinal ternal Mus:les replace both the 

 Primary and Secondary sets of Anax and Aeshna. In this respect 

 they are like those of Lestes, but in position they diverge slightly 

 caudad as in Anax. Each muscle is wider than long and forms 

 an undivided sheet. The larvae of Libellula, Plathemis, and 

 Sympetnmi are similar in respect to these muscles. 



The Secondary Longitudinal Sternal Muscles are absent. 



The Tertiary Longitudinal Sternal Muscles (plate XXI V^, fig- 

 ure 13, tis.) lie in the usual position with their ends just showing 

 along the sides of the median space occupied by the nerve cord. 



There are no Internal Tcrtiaries. 



Segmental Muscles of the Tergum: (Plate XXIV, figures 15 

 and 16)— 



The Primary Longitudinal Tergal Muscles (plate XXIV, figures 

 15 and 16, pit) are even wider than the corresponding sternals, 

 and seem to have the same structure, i.e., each is a broad thick 

 band. 



There are no Secondary Longitudinal Tergals. 



The Tertiary Longitudinal Tergal Muscles (plate XXIV, fig- 

 ure 16, tit.) ai-e well developed, increasing in size from the anterior 

 to the posterioi' segments but never being more than half the 

 length of their respective segments. 



The Quaternary Longitudinal Tergal Muscles are absent. 



The Quinary Longitudinal Tergal Muscles (plate XXIV, figure 

 16, qlt.) are short and l)i()a(l. They are on the lateral regions of 

 the tergum and arc thus not covered by the Primaries. 



Thoracico-abdominal Muscles: (Plate XXIV, figure 13) — 

 Both sets of these muscles are clearly shown in the figures. 

 They are like the rest of the longitutlinal muscles in being 



single plates. 



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



