LABIUM OF ANAX JUNIUS. 2QI 



with the thorax in the air. It seems to he during this restless 

 period that the labium is remodeled and retracted into the sub- 

 mental portion of the old skeleton, though it has been impossible 

 to observe the steps in this process. It is accomplished in a few 

 hours at most, perhaps in a much shorter time, as there appears 

 little evidence of profound histological change. Practically all 

 of the stages collected were similar to those illustrated in Figs. 2 

 and 3. The mentum and lateral lobes of the larval skeleton are 

 entirely empty and the labium has retracted into the basal two 

 thirds of the old submentum. Its parts are straightened out and 

 rolled laterally to fit the tube-like case, while the whole labium 

 stands out ventrally from the under side of the head. When 

 viewed under low magnification most of the parts of the adult 

 labium are visible but they are thicker and more fleshy in appear- 

 ance and are closely rolled together. The broad lateral and median 

 lobes are especially conspicuous. Attempts to flatten out the ex- 

 cised organ are not usually successful as the tissues are very 

 delicate and the parts tear badly. However, a median longitudinal 

 section dividing the labium into halves, made possible the de- 

 termination of the following facts. 



As all of the internal structures are so crowded together it is 

 difficult to make out their relations. However, the larger muscles 

 are quite clear as to identity. The primary flexor muscles are 

 very long and may be followed laterally around the bases of the 

 adductors as in the larva. Each is accompanied by a large, de- 

 generating trachea. The adductors have contracted to form very 

 short, thick muscles. They are curved ventrally at their origins 

 and insert as in the larva. They can be identified with assurance 

 by their insertion and relations to the primary flexors. The re- 

 maining muscles cannot be so definitely followed but may be seen 

 in general outline, tending towards vertical or slightly oblique 

 positions in the mentum and submentum. As these latter are so 

 rolled up, however, it is probable that the muscles might assume 

 diverging positions as in the adult, if the labium was flattened out. 



In the ventral, distal portion of the mentum are two rounded 

 masses of some size which suggest degenerating muscles. Com- 

 parison of the adult with the larva indicates the loss of the ab- 



