LABIUM OF ANAX JUNIUS. 293 



either side of this enlarged portion. The submentum is greatly 

 reduced but offers support for the origin of all of the larger 

 muscles (Figs. 4 to 7). The unique adaptations for extension 

 and flexion so marked in the larva are gone. 



Adult Musculature. 



There are five pairs of muscles in the imaginal labium. These 

 are greatly reduced in size and lack much of the precision of ad- 

 justment of the earlier condition. A comparison of the larval, 

 transitional, and adult structures has led to the following homology. 

 There is nothing 'to indicate that more than one pair has been 

 destroyed. Many are clearly identified by their attachments and 

 relations, while a few others have been difficult to determine ex- 

 cept by elimination and by evident function. They may be 

 located on Figs. 4 to /. 



Muscles Activating the Lateral Lobes. The abductors of the 

 lateral lobes. These muscles are missing in the imago. The two 

 rounded masses of apparently degenerating muscular tissue in the 

 transitional labium may represent them. Abduction of the lateral 

 lobes is now accomplished indirectly by the pull of the secondary 

 flexors on the squames. 



The adductors of the lateral lobes. This pair of muscles is 

 clearly in its larval position. The origin of each is upon the ven- 

 tral wall of the submentum just proximal to the hinge or angle. 

 The area of attachment is circular or oval in form, and is close 

 to the median line. The insertion is, as in the larva, upon a 

 strong tendon at the inner angle of the lateral lobe. This inner 

 angle is distinctly offset dorsally (i.e., towards the buccal cavity) 

 so that a contraction of the muscle produces flexion of both the 

 lateral lobe and the median lobe as well as adduction of the former. 

 In shape it is subcylindrical and tapers from its origin to its inser- 

 tion in a half spindle. It lies mesiad of other muscles and some- 

 what parallel to the primary flexor. 



Muscles Activating the Mentum and Submentum. The primary 

 extensor muscles are the longest in the adult labium. They are 

 of depressed spindle shape, and lie in the median line between the 

 bases of all the diverging muscles. In dissecting the labium free 



