46 THE TRACHEATION OF WINGS 



significant for the cause of the migration of the medial trachea along the 

 transverse basal trachea, as stated in the introduction, was one of the 

 problems which prompted this research. 



Modifications of the thorax which would result in the posterior migra- 

 tion of the wing process would also result in the posterior migration of the 

 base of the medial trachea. Likewise a cephalization of the wing would 

 bring the cubito-anal group of tracheae nearer the medial trachea, if the 

 wing process remained in its original position and did not allow the medial 

 trachea to move cephalad with the rest of the structures of the wing. 



The consideration of the relationships of thoracic peculiarities and the 

 modifications of the tracheae to the wings may profitably be extended to the 

 more general conditions. The insects considered in this paper have been 

 divided into three groups : those with generalized connections of the wing 

 tracheae, those with reduced connections of the wing tracheag, and those in 

 which the connections of the wing tracheae have been specialized by the 

 addition of new connections. In the group where the conditions of the 

 tracheal connections are generalized the thoracic structure is also general- 

 ized. The examples of the Blattidas among the Orthoptera, the Plecoptera, 

 the Neuroptera, the Lepidoptera, and the others are quite generalized, while 

 the Coleoptera and Hemiptera are mentioned both for their somewhat 

 generalized wing connections and for the reduced connections to the legs, 

 which latter condition is accompanied by the oblique position of the lateral 

 sclerites of the thorax. 



Among the insects with reduced connections of the wing tracheae there 

 are many varieties of thoracic structure illustrating several lines of speciali- 

 zation. It is not the purpose of this discussion to enter into the details of 

 so complex a region as the thorax or to attempt to ascribe all the modifica- 

 tions of the connections of the wing tracheae to the peculiarities of thoracic 

 structure alone, but rather to call attention to the fact that reduced wing 

 tracheae occur in the insects that have a specialized thorax. In the draw- 

 ings of the Ephemerida (Figs. 30 and 31) and the Hymenoptera (Fig. 32). 

 apodemes are represented by dotted lines just posterior to each wing. 

 These apodemes may be studied in insects which are about to emerge from 

 the pupal state and from their position it seems very probable that they 

 obstruct the course of the cubito-anal tracheae and eventually lead to their 

 reduction and the consequent cephalization of the air supply to the wings. 



The last group of insects, those with additional tracheal connections to 

 the wings, includes the Odonata (Figs. 34 and 35) and the jumping Orthop- 

 tera (Fig. 33). These two groups of insects are peculiar in that their nymphs 

 have their wing pads flexed dorsally, approximating the mid-dorsal line. 

 Such a position of the wingpads favors the enlargement of any median 

 tracheal connections such as the accessory connections to the wings (a. c-r) 

 and (a. cu-a) because the wingpads are drawn so close to the dorsal longi- 



