32 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 



abdomen is wholly destroyed with the transformation to the imago, 

 though, according to Whedon (1929), the dissohition is not completed 

 until some time after ecdysis of the adult, about three days in Anax 

 Junius. The adult musculature of the abdomen, as shown by Plateau 

 (1884) in Agrion, and as more fully described by Whedon (1918), 

 in both Zygoptera and Anisoptera (fig. 10 C, D), is surprisingly sim- 

 ple considering the various uses the adults make of the abdomen in 

 mating and &gg laying. The intersegmental muscles are short, well- 

 separated groups of fibers arising on the posterior part of the seg- 

 ment in front and inserting on the anterior margin of the segment be- 

 hind. These muscles, Whedon (1929) says, are derived from the small 

 outermost muscles of the larval abdomen. The sterna of the adult are 

 provided with small anterior and posterior muscles arising on the 

 terga, which probably are expiratory in function. Only in the pos- 

 terior genital segments in both sexes and the anterior genital segment 

 of the male is there a more elaborate musculature, perhaps represent- 

 ing newly formed muscles of the imago. 



The musculature of the dragonfly larval abdomen is of particular 

 interest in that it consists of two distinct sets of muscles, those of one 

 set being highly developed for purposes of the larva and destroyed in 

 the imago, those of the other set being carried over into the adult to 

 become the principal intersegmental muscles of the imaginal abdomen. 

 It would appear that there is thus no transformation of purely larval 

 muscles into imaginal muscles. Still more curious is the fact that the 

 principal musculature of the larval abdomen has the structure of the 

 usual intersegmental musculature of the abdomen in other insects. 

 The abdominal musculature, therefore, must be at an early stage of 

 development differentiated into larval muscles and prospective imagi- 

 nal muscles. 



The striking difference between the skeletal structure of the odonate 

 larval abdomen and that of the adult abdomen suggests that the pat- 

 tern of sclerotization in the insect integument is merely an adaptation 

 to mechanical function. Nevertheless, it would be of interest to know 

 what parts of the odonate larval abdominal integument become spe- 

 cific parts of the imaginal integument, if this could be determined at 

 the transformation by the method of scarring the larval integument, 

 as has been done in the case of the eyes and the thorax. 



Considering the extent of the skeletal and muscle changes that takes 

 place at the transformation from larva to adult in both the head and 

 the abdomen, the development of the wing muscles in the thorax, and 

 the reconstruction of the alimentary canal and tracheal system, the 

 total reorganization of the dragonfly during its transforming period 



