30 THE TRACHEATION OF WINGS 



dorsal view of the thoracic tracheae and represents the tracheae of both the 

 wings and legs extending laterad. It must be kept in mind that when the 

 thorax is viewed from the dorsal side the wings are directly above the legs 

 (Fig. 17, B). Since the conformation of some of the insects has made it 

 necessary to draw the dissections from the side view and others from the 

 dorsal view, the two diagrams are given to aid in the comparison of these 

 two different aspects of the thorax. 



There are three spiracles directly connected with the respiration of the 

 wings; one in each of the last two segments of the thorax and one in the 

 first segment of the abdomen (5^1, spo, and sps). The anterior and posterior 

 of these two spiracles (5^1 and 5^3) each contributes one tracheal branch to 

 the appendages of the mesothorax and the metathorax respectively. The 

 middle spiracle {sp^} contributes two branches; one to the mesothoracic 

 appendages and one to the metathoracic appendages. In this way each 

 wing and each leg receives two tracheal branches; one from the spiracle 

 anterior to it {c-r to the wing, and as to the leg) and one from the spiracle 

 posterior to it {cu-a to the wing, and ps to the leg.) This condition is 

 retained, in its essentials, in all the insects studied. Even tho the meta- 

 thoracic spiracle is absent in many of the more specialized insects, its 

 position is indicated by the rudimentary spiracular tnmk (Fig. 21, r. spi), 

 from which arise branches to the thoracic appendages, very much as in the 

 more generalized insects, where the metathoracic spiracle is well developed. 



As has already been stated, these branches that arise from the trunks at 

 the bases of the spiracles supply air to both the wings and the legs. The 

 leg tracheae are Y-shaped; each leg trachea being formed by the union of 

 two trunks. These trunlcs are designated as the anterior stem {as) and 

 the posterior stem (ps) respectively. In the more generalized insects the 

 branches to the wings arise from the stems of the leg tracheae, which form 

 the arms of the Y. The figure of the nymphal cockroach (Fig. 18) shows 

 that the tracheas going to the legs are much larger than those leading to the 

 wings. The relations of the leg and wing tracheae are such that it seems 

 very evident that the branches coming from the spiracles are primarily leg 

 tracheae and that the branches to the wings are secondary. 



In some cases the wing and leg tracheae arise separately from the 

 spiracles. Such a condition may be explained as the result of a divergence 

 of the bases of the two tracheae which has been carried so far that their 

 connections are entirely separate. However the more general relations 

 between the tracheae to the wings and those to the legs have been retained, 

 at least to some extent, in all of the insects studied. For this reason it 

 would seem that a consideration of the tracheae to the wings cannot ignore 

 the condition of the tracheae to the legs. If there is any preference as to 

 the air supply from the different spiracles which results in a modification of 

 the tracheae to the wings, some modification of the tracheae to the legs might 



