1918.] NATURAL SCIENCES OF PHILADELPHIA. 75 



THE RECTAL TRACHEATION AND RECTAL RESPIRATION OF THE LARVAE OF 



ODONATA ZYGOPTERA. 



I. RECTAL TRACHEATION OF ARGIA PUTRIDA LARVA. 

 BY ANNA M. CULLEN. 



Argia moesta pidrida Hagen is a Zygopterous dragonfly of wide 

 distribution throughout the eastern United States. Its larvae 

 occur in flowing streams, the material studied having been collected 

 at Cobb's Creek near Beechwood Park, Pennsylvania, May 25, 

 1914. The larva sectioned was killed in hot Gilson (BoUes Lee, 

 Microtomist's Vade Mecum, Third Edition p. 472). It was stained 

 with Delafield's haematoxylin and alcoholic eosin. The rectal 

 tracheation was studied from a series of paraffin sections extending 

 through the sixth, seventh, eighth and ninth segments of the larva. 



The alimentary canal in this region will be considered first. At 

 the beginning of the hind gut, in the posterior part of the sixth 

 segment, the epithelium has six deep longitudinal folds. In this 

 region the epithelium is somewhat thin. In the anterior half of 

 the seventh segment the alimentary canal is triangular in section. 

 This triangular appearance is caused by three patches of thickened 

 epithelium, one dorsal in position, the others right ventral and 

 left ventral. Between the three patches of thickened epithelium 

 are small areas of thin pigmented epithelium. Tracheae penetrate 

 the thickened epithelium. No tracheae enter the thin pigmented 

 epithelium. The alimentary canal in the posterior half of the 

 seventh segment and the beginning of the eighth segment is extremely 

 thin-walled. Toward the middle of segment seven the patches of 

 thickened epithelium disappear and the alimentary canal becomes 

 thin-walled and folded. At first the folds have no definite arrange- 

 ment but gradually six definite folds appear, three large ones alter- 

 nating with three smaU ones. The six folds soon become equal in 

 size and using the clock face notation of Tillyard, the folds occupy 

 the positions of 2, 4, 6, 8, 10, and 12 of the clock face. Toward 

 the posterior end of segment seven the folds gradually disappear 

 and the alimentary canal is thin-walled, and oval, almost rectangular 

 in outline. This part of the larva contains few of the smaller tracheae, 

 none of which approach the alimentary canal. In the anterior part 



