112 PROCEEDINGS OF THE ACADEMY OF [March, 



through the rectal epithehum without amj specialisation of the 

 tracheal supply of that region, and the exchange must be regarded 

 as being primarily one between the blood of the larva and the water 

 in the rectum, quite irrespective of the tracheal system, which is 

 bound to benefit sooner or later by the change." His idea based 

 almost entirely upon speculative grounds, perhaps can be better 

 justified after the detailed morphological work on the tracheal 

 supply has been done. His attempt, however, to correlate the 

 thickened folds of rectal epithelium of Zygopterous larva? with the 

 basal pads of Anisopterous larvae, especially as regards the elimina- 

 tion of carbon dioxide, are, perhaps, not so well founded. The 

 detailed morphological work has shown that these folds are the 

 definite cellular parts of the rectum and have a tracheal supply. 

 The great quantities of spongy tissue present between the folds 

 suggests the supposed function attributed by Tillyard to the folds 

 themselves, viz., the elimination of carbon dioxide. 



Conclusions. 



1. Zygopterous larvae breathe by means of the rectum from 

 the time of hatching until transformation. 



2. Caudal "gills" serve only in a mechanical way, as rudders 

 in the locomotion of the larvae. 



3. Respiration through the skin of the larva is doubtful, but 

 if it takes place, is only in a very slight degree, not supplying enough 

 oxygen for the respiratory needs of the larva. 



4. Regular rhythmic contractions of the rectum take place 

 throughout the aquatic life of larvae. 



.5. Rhythm of rectal contractions is not interfered with by 

 removal of the caudal "gills." 



Bibliography. 



Calvert, P. P.— 1915. Studies on Costa Rican Odonata. VII. The 

 Waterfall-Dwellers: The Internal Organs of Thaumatoneura larva and the 

 Respiration and Rectal Tracheation of Zygopterous larvae in general. Ent. 

 News, XXVI, pp. 385-395, 435-447, Pis. XV-XVIl, I text figure. November, 

 December. (As this paper contains a bibliography, the titles of the works of 

 earlier authors are not listed here.) 



Carroll, M. — 1918. The Hind-gut, Abdominal Tracheae and Rectal 

 Respiration in the larva of Mecistogaster modestus from Costa Rica. Pro- 

 ceedings, Academy of Natural Sciences of Philadelphia, LXX, pp. 86-103. 



CuLLEN, A. M. — 1918. Rectal Tracheation of Argia putrida larva. The 

 same Proceedings, LXX, pp. 75-81. 



Jamieson, J. P. — 1918. The Tracheal Supply of the Rectum of the Larva 

 of Argia talamanca from Juan Vinas, Costa Rica. The same Proceedings, 

 LXX, pp. 81-85. 



