334 THE WINGS OF LEPIDOPTERA 



protodice. But in a considerable number of these insects the radial fork is 

 evident; but in these the free part of vein Ri has the appearance of 

 being a cross-vein (Fig. 340). 



In all pupal wings of the Frenatse the trachea of the radial sector of the 

 hind wings is reduced to an unbranched condition; but in many cases 

 trachea Mi has been transferred to it (Fig. 341) ; this is correlated with the 

 atrophy of the main stem of media in the adult, which is discussed later. 



The reduction of media to a three-branched condition. — In the Frenatas 

 as in the Jugatas the media of both fore and hind wings has been reduced to 

 a three-branched condition. 



It is quite possible that this reduction has taken place independently in 

 the two suborders ; for the separation of these suborders doubtless occurred 

 very early in the course of the evolution of the Lepidoptera. For this 

 reason, in attempting to determine the manner in which this reduction has 

 taken place in the Frenatae I submit only data drawn from the study of 

 representatives of this suborder. 



A study of the method of branching of media in the Frenatae shows that 

 the reduction of this vein is the result of the loss of vein M4 as a distinct 

 vein. There is no reason to believe that this vein has atrophied ; the reduc- 

 tion has doubtless been brought about either by the coalescence of veins 

 M3 and M4 or by the coalescence of veins M4 and Cui. 



One naturally turns to a study of the tracheation of the wings of pupae to 

 find a solution of the problem ; but in none of the many lepidopterous pupae 

 examined is media more than three-branched ; this suggests the conclusion 

 that veins M3 and M4 have coalesced. But in the course of a renewed 

 investigation of this subject I have found data that lead me to believe that 

 the reduction of media in this suborder is a result of the coalescence of veins 

 M4 and Cui, and that consequently the vein that has been commonly 

 designated as vein Cui is really vein M44-CU1. 



The nature of this data is well-shown by the tracheation of the wings of 

 Pieris rapes. In the hind wing (Fig. 341) there are, in addition to the 

 tracheae that are the anlagen of the principal veins and their branches, two 

 short trachea; designated in the figure as r-m and m-cu, respectively. 

 Trachea r-m is obviously a vestige of a secondary connection between the 

 medial and radial tracheas. Note that what is here considered as trachea 

 r-m arises from trachea R^ and that trachea Mi arises from trachea r-m a 

 considerable distance from its base ; the letters r-m in the figure are placed 

 at the tip of this trachea. This connection was probably, at first, trans- 

 verse, occupying the position of the cross-vein r-m in more generalized 

 wings, as in the fore wings of Prionoxystus (Fig. 343) and in the hind wing 

 of Packardia (Fig. 348). Correlated with a lessening of the air supply 

 through the main stem of the medial trachea, or with whatever the cause 

 may be that results in the atrophy of the main stem of vein M, the base of 



