1918.] NATURAL SCIENCES OF PHILADELPHIA. 81 



areas of Anisopterid larvae seems to strengthen this view. In the 

 rectal gills of these larvae, the minute branches of the trachess are 

 separated from the water of the rectum by a very thin epithelium. 

 This seems to show that respiration takes place most actively through 

 a thin epithelium. 



II. THE TRACHEAL SUPPLY OF THE RECTUM OF THE LARVA OF 

 ARGIA TAI;AMANCA FROM JUAN VINAS, COSTA RICA. 



BY JANET P, .TAMIESON. 



The rectal epithelium of the water-fall dweller, Argia talamanca, 

 presents three main longitudinal folds, one that is "dorsal and a 

 little to the left of the median plane," a second that is "left latero- 

 ventral" and the third that is "right lateral." These folds (Fig. 1.) 

 correspond in position with those of the water-fall dweller 

 Thaumatoneura described by Calvert {Entomological News, Vol. 

 XXVI, p. 387, and plate XVII, fig. 1.) Those of A. talamanca are, 

 however, deeper as may be seen by comparing photographs of the 

 transverse sections, and show a greater complexity. In some 

 parts of the rectum the free edges of the three folds appear to meet 

 in the center of the lumen of the gut. Between the bases of these 

 primary folds the epithelium thins out and becomes darkly pigmented. 

 From the base of each primary fold, is given off a secondary shallower 

 fold, to the right in the case of the dorsal fold, to the left in the case 

 of the left latero-ventral fold and ventrally in the case of the right 

 lateral fold. 



Toward the hind end of the rectum the secondary folds disappear 

 and the main folds have practically no depth; this gives an almost 

 cylindrical shape to the hind part of the rectum. 



The larva of Argia putrida from the vicinity of Philadelphia, 

 described in the preceding paper by Miss Cullen, differing from 

 A. talamanca in that it lives in streams of continuously flowing water, 

 shows three simple shallow folds in the rectal epithelium, one dorsal, 

 one right lateral and one left lateral. The epithelium is much denser 

 and thicker than in this water-fall dweller of the same genus, and 

 the thin pigmented areas between the bases of the folds are not 

 so broad. 



It has been suggested by Calvert that the more extensive surface 



area afforded by the greater folding of the rectum together with 



the thinner, less dense nature of the epithelium of the water-fall 



dwellers may aid these larvae materially in procuring a supply of 



6 



