NORTH AMERICAN ODONATA. 171 



Correlated with their presence, as already mentioned, is the excava- 

 tion of the anal border of the hind wings. In the females of many 

 Gomphinse, rudimentary, non-denticulated auricles exist. 



The abdomen of the females is terminated by two unjointed dorsal 

 appendages, belonging to the tenth segment, and therefore homolo- 

 gous to the superior appendages of the males. Their shape varies 

 but little in different Odonata, and they are not known to perform 

 any function. The anal segment lies below the appendages. 



The accessory genital organs of the male and the vulvar lamina 

 of the female will be described in connection with the reproductive 

 organs. 



THE MUSCLES. 



The muscles of the Odonata are well developed, usually consisting 

 of a number of fasciculi. Their attachments, whether of origin or 

 insertion, may be direct or by tendon. The tendons are chitinous, 

 and are usually oif one of two kinds ; in the one, the tendon is dark- 

 colored and forms a stalked, abruptly flattened cup, to whose concave 

 surface the muscle fibres are attached ; in the other the tendon is 

 pale in hue and conical in shape, receiving the muscle fibres at its 

 wider end. 



Where possible, the muscles described below have been identified 

 from the general description of insectan muscles by Burmeister (32), 

 and from Lendenfeld (4), Poletaiew (5), and Plateau (11). The 

 chief species which has served for this account is Aeschna constrida 

 Say, but comparisons have also been made with Calopteryx and Li- 

 bellula. Only the most important muscles are included. 



Cephalic muscles.— The muscles which move the eutire head are very 

 small. They arise from the anterior part of the mesothorax, and from the pro- 

 thorax, and insert near the margins of the posterior cephalic foramen. Those 

 dorsally placed elevate the head and draw it backwards, while the ventral ones 

 depress it; the lateral ones draw it to either side. 



Abductor labri (Burm.) arises by flat tendon from point of union of fious and 

 vertex, passes downwards immediately behind and in contact with the posterior 

 border of the shelf (c) separating the clypeus from the frons, and inserts without 

 a tendon, into the base of the labrum close to the middle line; it elevates the 

 labrum ; the right and left abductors lie side by side. 



Adductor labri (Burm.) arises in common with, but on the outer side of the 

 abductor of the same side, but forms a distinct belly and inserts in the mem- 

 branous roof of the mouth behind the labrum, and farther from the middle line 

 than the preceding; it draws the labrum downwards and backwards. 



Adductor mandibulse {flexor mandibtdse Burm.) large, fan-shaped, arising from 

 the upper part of the posterior surface of the head from near the mid-dorsal line 



TRANS. AM. ENT. SOC. XX. JULY, 1893. 



