xxxiii, '22] ENTOMOLOGICAL NEWS 303 



the tracheal branch of R which supplies a part of the course 

 of the imaginal vein Rs, appears as a secondary outgrowth 

 whose purpose is to function as a part of the tracheal supply of 

 a vein which for some reason has failed to receive a tracheal 

 supply from the one of which it is properly a branch, the media. 

 Unless we interpret Rs as a supplementary vein not homologous 

 to any primitive one, we must accept the theory of Tillyard and 

 consider it as a true branch of the media. As to the fate of the 

 original Rs, the ontogenetic stages in the larva seem to indicate 

 that, at least the tracheae corresponding to this vein, remain 

 along the course of A*!, and that possibly the vein Rs has com- 

 bined with Rl or has taken its place. This is the conclusion we 

 should arrive at if we trusted in the ontogenetic stages to obtain 

 a true account of phylogeny. However, I believe that our faith 

 in such evidence should not be too implicit and that conclusions 

 derived therefrom should not be accepted unless supported by 

 other evidence which may develop out of a paleontological 

 study. 



BIBLIOGRAPHY. 



COMSTOCK, J. H., and NEEDHAM, J. G., 1898, The Wings of Insects. 

 Amer. Nat, XXXII and XXXIII, 1898 and 1899; Art. Odonata, 



XXXII, pp. 903-911, 9 figs. 



XEEDHAM, J. G., 1903, A Genealogic Study of Dragon-Fly Wing 

 Venation. Proc. U. S. Nat. Mus., XXVI, pp. 703-764, Plates xxi- 

 liv. (No. 1331). Wash., U. S. A., 1903. 



TILLYARD, R. J., 1922, New Researches upon the Problem of Wing- 

 Venation of Odonata. I. A Study of the Tracheation of the Larval 

 Wings in the Genus Uropetala from New Zealand. Ent. News, 



XXXIII, pp. 1-7, 45-51, Plate I. 



EXPLANATION OF PLATE XI. 



Figs. 9-13, Wing rudiments from larvae of Gomphus villcsipcs. 

 Fig. 9, Length of larva 8 mm., length of wing 0.12 mm. 

 Fig. 10, Length of larva 7 mm., length of wing 0.15 mm. 

 Figs. 11-12, Length of larva, 10 mm., length of wings 0.23 mm. 

 Fig. 13, Length of larva 12 mm., length of wing 0.4 mm. 

 Fig. 14, Wing rudiment from larva of Gomphus e.vilis; length of 

 larva 10 mm., length of wing 0.45 mm. 



