THE WINGS OF EPHEMERIDA 



215 



the venation is so similar that there is not the sHghtest difficulty in tracing 

 the homologies of the veins. In one, the radial sector and the media contain 

 well preserved tracheae; in the other, there is not the slightest trace of a 

 trachea in these veins. On the other hand, in the latter, the cubital trachea 

 is forked, one of the branches traversing vein Cu^; while in the former, the 

 cubital trachea is simple." 



Our knowledge of the tracheation of the wings of May-flies remained in 

 the unsatisfactory condition indicated above until quite recently; when 

 Miss Anna H. Morgan published the results of an extended study of the 

 tracheation of the wings of insects of this order (Morgan '12). 



In the course of this study Miss Morgan examined with great care the 

 wings of a large number of nymphs, representing fifteen genera. These 



Fig. 214. — Hypothetical type of tracheation of wings of 

 insects. 



were Epeorus, Iron, Arneletus, Ephemera, Blastiiriis, Hexagenia, Polymi- 

 tarcys, Ephemerella, Siphlurus, Callihcstis, Ckirotonetes, Heptagenia, Lepto- 

 phlebia, Choroterpes, and Ccsnis. Figures showing the tracheation of the 

 wings of these nymphs and of the venation of the wings of the adults of the 

 same genera are given in her paper. 



This work was done in the entomological laboratory of Cornell 

 University; and its progress was carefully followed by Dr. Needham 

 and myself. We both accept Miss Morgan's conclusions, although in 

 some respects they differ from those that we have published; and the 

 homologies of trachea) and wing veins indicated later are based on her 

 conclusions. 



The basal connections of the irachccE of May-flies differ, as was shown 

 by Comstock and Needham ('99), from those of all other insects in which 

 they have been examined. In the May-flies a single large trachea enters 

 each wing (Fig. 215). This trachea arises from the spiracular trunl-c of one 

 side of the thorax and, after giving off a branch to the corresponding leg. 



