THE TRACIIEATION OF WINGS 



17 



members of the family Blattidae of the Orthoptera, there are two distinct 

 groups of tracheae that enter the wing; these we designated as the costo- 

 radial group and the cuhito-anal group respectively. In these insects the 

 medial trachea is a member of the costo-radial group (Fig. 6). 



In all other forms that we studied, except the Ephemerida, a transverse 

 trachea connects these two groups of wing trachea;; the position of this 

 transverse basal trachea of the wing is indicated in the figure (Fig. 6) by 

 dotted lines.* Frequently the transverse basal trachea is indistinguishable 

 from the two main trunks which it connects, the three forming a single, 

 continuous, transverse trachea, from which arise all of the wing tracheae 

 (Fig. 7). All of the stages of this development were found by us within 

 the Orthoptera. 



We also found that when a transverse basal trachea is formed, the 

 medial trachea tends to migrate along it toward the cubito-anal group of 



Fig. 7. — \Yings of an acridid nymph (After C. & N.). 



tracheae, and often becomes united with that group. This is well shown in 

 certain Orthoptera and in the cicada. In some cases the base of the radial 



*More recently it has been found that in certain Homoptera, the Membracidae 

 and the Jassidas, the same generalized condition of the basal connections of the wing 

 tracheae exists as in the Plecoptera. 



