218 



THE WINGS OF EPHEMERIDA 



In the Odonata, where the area of the radial sector has been occupied by 

 some of the branches of media, the complete history of this invasion can be 



Fig. 217. — Wing of nymph of Heptagenia inlerpunctata 

 (After Morgan). 



seen by a study of the ontogeny of representatives of the suborder Anisop- 

 tera, as is demonstrated in the discussion of the wings of that order. Here 

 the radial sector is preserved as an unbranched vein; and it retains its 

 connection with the main stem of radius, although it occupies a position 

 between certain of the branches of media, usually between veins M2 

 and M3. 



In the suborder Zygoptera the distal portion of the radial sector is as 

 well preserved as in the Anisoptera; but in this suborder the trachea Rg 

 has lost its connection with trachea R and has become joined to the medial 

 trachea. 



With this evidence of the switching of the base of the trachea Rg to the 

 medial trachea in the Zygoptera it is not difficult to believe that the invasion 

 of the radial area by media in the Ephemerida has produced a similar result. 



Fig. 218. — Wing of adult Heptagenia inter punctata 

 (After Morgan). 



The truth of this conclusion would be finnly estaljlished if one could 

 find generalized May-flies in which trachea R^ retains its connection with 

 trachea R. The search for such forms was made by Miss Morgan, and 

 resulted in the finding of one species in which the connection of trachea Rg 

 with trachea R frequently exists. This insect is Heptagenia inter punctata. 

 A large number of the wing-pads of this species were examined ; half of the 



