20 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I23 



chamber should be referred to the colon, and that the end chamber 

 is the true rectum. The anus opens between three small circumanal 

 lobes at the bases of the caudal prongs (fig. ii G). 



At the final metamorphosis of the larva there takes place a total 

 reconstruction of the alimentary canal, details of which have been 

 described by Straub (1943). In the stomodaeum and proctodaeum, 

 after the shedding of the larval intima, reconstruction takes place 

 apparently as in the external parts of the ectoderm by renewed and 

 differentiated growth of the epithelium. In the mesenteron, on the 

 other hand, the larval epithelium itself is cast off and the imaginal 

 epithelium is formed anew from basal regeneration cells, as in most 

 holometabolous insects. At the larval moults, however, Straub finds 

 no evidence of a renewal of the mesenteron epithelium. 



Dph Ilm rspC(Cln) 



Hphy Lb Cr Prvent Vent Mai tmcl 



Fig. 7. — Anux Junius (Drury), the larval alimentary canal. 



Cb, cibarium ; Cln, colon ; Cr, crop ; Dph, transverse muscular diaphragm ; 

 Hphy, hypopharynx; Ilm, ileum; Lb, labium; Mai, Malpighian tubules (not 

 fully shown); Oe, oesophagus; Prvent, proventriculus ; Red, rectum; rspC, 

 respiratory chamber; tincl, transverse muscle; Voit, ventriculus. 



IV. THE THORAX 



The thorax of the dragonfly larva is characterized by three special 

 features (fig. 8 A). First is the obliquity of the mesothoracic and 

 metathoracic pleura as indicated by the posterior slant of the pleural 

 sulci from the leg bases to the wings. Second is the almost complete 

 union of the adjoining pleural plates of the wing-bearing segments, 

 resulting in the suppression of an intersegmental groove between the 

 epimeron of the mesothorax and the episternum of the metathorax. 

 Third is the dorsal extension of the upper plates of the mesothoracic 

 episterna (EpS2) until they meet along the midline of the back in 

 front of the wings, and the corresponding downward extension of the 

 metathoracic epimera (Epnh) on the ventral surface behind the legs. 

 These features of the thorax evidently have no particular functional 

 significance for the larva, since the larva uses its legs in the ordinary 

 manner for locomotion, and its wings are entirely passive rudiments 

 of the future organs of flight. On the other hand, the thoracic struc- 



