436 RECTAL GILLS IN LARViE OF ANISOPTERID DRAGONFLIES, 



the nitrogen to be considerably in excess of its normal propor- 

 tion in atmospheric air (partial pressure of N in tracheal gas = 

 about 90% of total pressure). Further, the total pressure within 

 the tracheae of such an insect exceeds the atmospheric pressure 

 very considerably (according to Lowne, it equals 810 mm.). 

 Thus the partial pressure of nitrogen would be 90% of 810 mm., 

 i.e., 729 mm., against 600 mm. for atmospheric air. Is it likely 

 that similar results would be obtained for our aquatic larvsel I 

 think not. We might rather expect that the proportion of 

 nitrogen to oxygen in the tracheae of these larvae would more 

 nearly approach the ratio of the amounts of these gases dissolved 

 in the water. If a ratio approaching to this latter could be ob- 

 tained by analysis, it would strongly support the Diffusion- 

 Theory. So far, I have not succeeded in devising an apparatus 

 suitable for the necessarily very delicate analysis required, but I 

 hope to carry this out on some future occasion. 



BIBLIOGRAPHY. 



1. Calvert, P. P. — '* The first Filling of the larval Tracheae with Air." 



Ent. News, Philadelphia, 1898, p. 73. 



2. Dewitz, H. — *' Einige Beobachtungen, betreffend das geschlossene 



Tracheensystem bei Insecten-larven." Zool. Anz., 1890, xiii., pp. 

 .500-504, 525-531. 



3. Lowne, B. T. — The Anatomy, Physiology, Morphology, and Develop- 



ment of the Blowfly. London, 1893-5. (Vol. ii., pp.373-386). 



4. Purser, G. L. — " Preliminary Notes on some Problems connected with 



Respiration in Insects generall}', and in Aquatic Forms in par- 

 ticular." Proc. Camb. Phil. Soc, xviii., 1914, Part 2, pp.63-70. 



5. Ris, F. — "Die Atmungs-Organeder anisopterenLibellenlarven." Mitt. 



Schweiz. ent. Ges., Berne, 19L3, Bd.xii., Hft.2, pp.25-41. 



6. Sadones,J. — * 'L'Appareil digestif et Respiration larvairedesOdonates." 



La Cellule, Louvain, 1896, xi., pp.273-324, 3 plates. 



7. TiLLYARD, R. J. — "The Hatching of the Larva of Anax paputnsis 



Burm." British Assocn., Australian Meeting, Sydney, Aug., 1914. 



8. "On the Rectal Breathing-Apparatus of Anisopterid 



Larvae." Trans. Linn. Soc. London, 1915. [Publication delayed 

 by the War]. 



