BY Ft. J. TILLYARD. 165 



A. A branch from the great dorsal trunk enters tlie costal 

 side of the wing-base and supplies the costo-radial i^i-oup of wing- 

 trachefe (viz., cosfa^ subcosta, radius and media). 



B. A branch from the venti-al trunk entei's the anal side oi the 

 wing-base and supplies the ciibi to-anal group of wing-tracheae 

 (viz., cubitus and analis). 



In all cases, except riecoptera and some Cockroaches, the 

 branches A and B are connected by a transverse trachea, so that 

 a continuous loop is formed passing from the dorsal trunk into 

 the costal side of the wing-base, thus making a loop projecting 

 slightly into the wing-base (from this loop the wing-trachese arise 

 in order), and finally leaving the wing-base at its anal side and 

 joining the ventral trunk. 



It is quite clear, therefore, from the start, that this last con- 

 nection with the ventral trunk could not exist in Odonate larvae; 

 since this trunk does not enter the thorax. However, it is 

 equally clear that a complete loop exists in the Imse of the wing- 

 rudiment, since it can be seen both in the living larvae, and in 

 the cut-oif wing-cases. I propose to call this loop tlie alar trunk 

 (AT), since it is the trachea from which all the principal longi- 

 tudinal tracheae of the wing arise. The question of its connec- 

 tions costal ly and anally with the general tracheal system, will 

 be fully dealt with in Part ii. of this paper. 



It is fitting that I should state here how valuable and inspir- 

 ing I have found Professor Needham's work, already quoted. It 

 is, indeed, a solid and excellent foundation, on which all future 

 researches on Odonate wing- venation must be built, and a work 

 that merits the highest meed of praise. Nor can I pass on with- 

 out recording my indebtedness to all those who, during my long 

 period of ill-health, have so generally assisted me in obtaining 

 the many rare larval forms necessary for the work in hand. For 

 these, I have to thank my wife, Mr. F. W. Carpenter, M.A., 

 Mr. Gregory Geake, and my brother, Mr. S. J. Tillyard. 



Owing to the fact that the wing-cases of so many larvie are 

 very deeply pigmented, and .sometimes also very hairy, I have 

 adopted the plan of illustrating this paper by drawings traced 



