2 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 23 



In the dragonfly larva there is none of those special regeneration 

 centers, or "imaginal discs," that in insects of higher orders form the 

 adult tissues from latent embryonic cells while the larval tissues go 

 into dissolution. The special adult structure of the skeleton of the 

 dragonfly, for example, is formed simply by a renewed activity in the 

 larval epidermis during the transformation period that produces an 

 entirely different skeletal structure from that which this same epi- 

 dermis produced many times before at the larval moults. A change 

 of the same nature takes place in the ectodermal parts of the alimen- 

 tary canal, though the imaginal mesenteron is regenerated in the usual 

 manner from replacement cells. Muscles of the larval head and ab- 

 domen go into dissolution, and are replaced by muscles suitable to the 

 adult, but the thoracic wing muscles simply complete their develop- 

 ment, while the wings themselves rapidly take on the adult form and 

 venation. 



The metamorphic changes that take place in the dragonflies are un- 

 doubtedly, as in other insects, controlled by hormones, though the 

 dragonfly has been neglected as a subject for hormonal study. Cor- 

 pora cardiaca and allata are both present in the Odonata. The first, 

 according to Cazal (1948), lie on the lateral walls of the aorta behind 

 the brain and are fused with each other above the aorta ; they receive 

 the usual four nerves from the brain, and are best developed in large 

 larvae and adults. The corpora allata, Cazal says, are globular or 

 ovoid bodies in young larvae, but in the adult they become elongate 

 and lie in contact with the circumoesophageal nerve connectives. They 

 are innervated through the anterior ends of the corpora cardiaca. In 

 addition to these dorsal incretory organs, small glandular bodies lying 

 ventrally in the posterior part of the head have been described by 

 Pflugf elder (1938, 1947) in Odonata and other insects. They are 



Fig. I. — Anax Junius (Drury), larva (x i|). 



