82 



PROCEEDINGS OF THE ACADEMY OF 



[March, 



oxygen from the rectum that supplements the supply obtained by 

 the gills when the larva is in the water. The caudal gills of A. 

 talamanca are much shorter than those of A. putrida. This suggests 

 that there may be a definite ratio between the shortness of the gills 

 and the complexity of the rectal epithelial folds. This theor^^ is 

 strengthened by the fact that Anisopterous larvse, as described 



dim 

 rdrti 



cf 

 rdt 



rlpa 

 rlrf 



rlrli 

 ml 



vim 

 rlt 



va — 



Fig. 1. Transverse section of abdominal organs of larva of Argia talamanca 



9 near the hind end of the 8th segment (TS. 12 of row 6, slide 2), seen from 



its anterior face. Cuticle and hypodermis removed before embedding, also 



on the left side (right in the figure) the longitudinal muscles. Photographed 



by Mr. H. A. Walters, using Leitz ocular 4, objective 3. Enlarged 85 diameters. 



cf, connective tissue and fat. 

 dim, dorsal longitudinal muscle. 

 drf, dorsal rectal fold. 

 dv, dorsal vessel. 

 Idrti, left dorsal rectal trachea. 

 Idt, left dorsal trachea. 

 llpa, left lateral pigmented area. 

 llrf, left latero-ventral rectal fold. 

 llrt, left lateral rectal trachea. 

 lit, left lateral trachea (lies outside 

 of the field of this figure). 



mt, Malpighian tubule. 



mvpa, mid-ventral pigmented area. 



r, rectum. 



rdrti, right dorsal rectal trachea. 



rlpa, right lateral pigmented area. 



rlrf, right lateral rectal fold. 



rlrti, right lateral rectal trachea. 



rdl, right dorsal trachea. 



rlt, right lateral trachea. 



va, vagina. 



vim, ventral longitudinal muscle. 



