1G4 DEVELOPMENT OF THE WING-VENATION OF ODOXATA, 



Now Needham's paper deals with i. only, and that chiefly in 

 SO far as it concerns the Anisoptera. The investigations into 

 the Zygoplera seem to have been on a much smaller scale, and 

 it is very evident that a wide field of research remains open in 

 this direction. With regard to the Anisoptera, it seemed to me 

 that the study of the anal tracheae had been left in a somewhat 

 unsatisfactory state. Hence I have devoted a considerable part 

 of my paper to an elucidation of this problem, with special refer- 

 ence to the development of the so-called mial loop. 



With regard to ii , it seems quite clear that the wing-venation 

 cannot be fully understood until we go to the root of the problem. 

 That is to say, we must go a stage back beyond i., and enquire 

 carefully how the oxygen-supply is brought to the wing-tracheae; 

 or, in other words, we must connect up these wing-tracheae witli 

 the complex tracheal system of the larva, and study the connec- 

 tion between them. 



The general tracheal system of the Odonate larva is so peculiar 

 that it might v.ell be suspected of exercising some special influ- 

 ence on the developing wing. Its chief peculiarity is the fact 

 that the oxygen-supply is derived in all cases from the anal end 

 of the body during practically the whole period of growth; either 

 by means of the internal " branchial basket " in the rectum of 

 Anisoptera, or by the external caudal gills of Zyyoptera. Hence, 

 chiefly by means of the huge dorsal tracheal trunks, but also in 

 a less degree by the visceral and ventral trunks, the oxygen is 

 conveyed forwards to all parts of the body. As regards the 

 head and thorax, the supply comes entirely from the dorsal 

 trunks, since the ventral trunks do not reach so far forward, and 

 the visceral trunks send only their attenuated anterior ends into 

 the thorax to connect with the tracheae of the middle leg. 



Now in all cases so far investigated, the tracheal suppl}'^ of the 

 developing wings of insects has been found to arise from two 

 sources*: — 



* Comstock and Needham, " The Wings of Insects," American Natural- 

 ist, xxxii. , pp.45 tt seq., 1898. 



