290 THE CANADIA.N ENTOMOLOGIST. 



times as the outer margin of the humeral cell, fusing above with 

 subcostal. The movement here is longitudinal, from base of wing out- 

 wardly to external margin. On the primaries some of the most 

 specialized forms of Pierids and Lyci^nids have only three branches 

 remaining. On the hind wings the radius is already two- or one-branched; 

 the remainder of the five primitive branches have been lost in the higher 

 lepidoptera, but retained in Hepialus and the Micropterygides. The 

 details of the process by which the radial branches of the fore wings have 

 been reduced in number become api)arent through a comparison of their 

 present position in the various genera. 



The branches of the media, 



which, as a rule three in number, alone survive of the system, are 



situated between cross-vein and outer margin of the wing. The base of 



the median system, as shown by Comstock, has disappeared and is again 



only exhibited in the Tineides. Tiiis base consisted of two, at least, 



longitudinal veins, which traversed the discal cell, and the traces of 



which are now to be found in certain backward spurs which remain 



attached to the cross-vein on its inner side. The reduction has taken 



place from the base outwardly. The branches themselves move upwardly 



or downwardly, attaching themselves to the system of the radius or that 



of the cubitus ; the cross-vein degenerating as a further stage in the 



disappearance of the median system. For this is doomed. The wing 



tends to divide into two halves — the radius and its system, the cubitus 



and its system. To the first belongs naturally, by position, the subcostal 



vein ; to the latter, the anal veins. The most perfect examples of this 



reduction are found in the Attacinse. Take our common Samia cecropia 



or Philosoviia cynthia. Here the cell has opened, the discal cross-vein 



has vanished, the branches of the media have attached themselves to the 



radial and cubital systems, deriving their nutrition from these, and the 



wing is centrally opened, from external margin to base, and free from 



veins. It presents now a certain coincidence with the embryonal or 



pupal wing, which is in itself curious, but need not detain us. We must 



finally notice the fact, that sometimes the branches refuse to follow the 



attraction of the upper and underlying systems. It is the middle or 



second median branchlet which is decisive. When this becomes radial, 



it follows the first median branch and attaches itself to the radial system. 



When it becomes cubital, it follows the third median branch and attaches 



itself to the cubital system. But sometimes it remains neutral. It will 



