THE TRACHEATION OF WINGS 47 



tudinal trachcce. On the other hand, the original tracheae {cii-a and c-r) 

 must be greatly elongated and no doubt are obstructed by apodemes 

 along their new path, especially in the case of Odonata. 



The accessory cubito-anal trachea (a. cu-a) of the Odonata is much 

 larger than the reduced cubito-anal trachea {cu-a) and is also larger than 

 either of the anterior tracheal connections {c-r and a. c-r) , each of which is 

 about half its size. The fact that the two anterior tracheae have had their 

 courses altered by the change in form isprobably the cause of their reduction. 



Some of the most interesting correlations between thoracic structure 

 and tracheal conditions are to be found in the study of the leg tracheae and 

 the analogy with the conditions of the wings is most instructive in the 

 consideration of their tracheae. In the Coleoptera (Fig. 25) where the 

 thorax is oblique and the legs have moved caudad, the anterior stem {as) 

 to the mesothoracic leg (/o) is absent and the anterior stem to the meta- 

 thoracic leg {h) is small while both of the posterior stems are large. 



The Hemiptera (Figs. 22, 23, and 24), which have a thorax like that of 

 the Coleoptera, also have modified conditions of the leg tracheas which are 

 most marked in the Belostomidae (Fig. 24) where there is a single stem of the 

 leg trachea, due to the posterior migration of the main leg trachea which 

 results in the obliteration of the posterior stem and the elongation of the 

 anterior stem of the trachea. 



The Odonata present a thorax which is oblique in the opposite direction 

 from the examples mentioned above, for the legs have moved cephalad. 

 This skewness of the thorax in the Odonata was studied by Needham and 

 Anthony {Journal of the New York Entomological Society, 1903, xi: 117- 

 125) and the angle formed between the perpendicular and the humeral 

 angle was found to vary from 21 degrees in some of the Aeschninas to 71 

 degrees in certain Agrioninae. This furnishes a series of modifications in 

 which the tracheae may be studied and it has been found by a study of a 

 series of n^onphs that the proportionate size of the anterior stem of the leg 

 trachea varies in direct proportion to the size of the angle of the thorax, 

 while the size of the posterior stem of the leg trachea varies in inverse 

 proportion to the size of the thoracic angle. The thoracic angle of Anax 

 Junius (Fig. 34) is 27 degrees and the posterior stem of the leg trachea {ps) 

 is slightly larger than the anterior stem {as) . Lestes (Fig. 35) has a thoracic 

 angle of 66 degrees and the posterior stem of the leg tracheae {ps) is very 

 small while the anterior stem {as) is comparatively large. 



In this connection it is interesting to note that Tillyard (1. c. p. 205) 

 entirely overlooked the posterior stem of the leg trachea in his figure of 

 Ausirolestes. The Odonata, therefore, with their highly modified thorax 

 and greatly altered tracheas to both the wings and legs, present the best 

 example of the correlation between thoracic structure and the tracheal 

 connections. 



