90 NATURAL 8CIENCE [February 



movable veins and show the general progress of their evolution. 

 The characters which we find in the movable veins are then 

 secondary, since they are recurrent, exhibited by the varying positions 

 of the veins, but always exhibited in a greater or less degree, and 

 thus opposed in value to the fixed subprimary character of the 

 internal vein of the Papilionides, which is of higher importance and 

 points to a diphyletic origin for our day butterflies. 



An extended comparison of the wings of butterflies and moths, 

 shows us that the main movement lies with the media and its 

 branches. The theory of the media and its system, based on its 

 characters in the moths, is, that it was formerly, as it is now in 

 Hepialus, an independent system, with its root in the base of the 

 wing. That portion which formerly connected the cross-vein with 

 its base, has vanished in most lepidoptera, leaving its traces, in the 

 shape of longitudinal scars, on the membrane of the median cell. 

 The cross-vein remains as a base or support for the three remaining 

 branches ; and, at first continuing to supply with nutriment these 

 three branches, tends ever to yield to disintegration and set them 

 free. Thus the original movement which led to the loss of the base 

 of the median system is still in operation. After the disintegration 

 of the base, it next attacks the cross-vein. After the cross-vein has 

 disappeared, it next attacks the branches. If these remain in their 

 original position, relying upon the cross-vein, they submit in turn to 

 the process of obliteration, from want of support, supply, and con- 

 nection, and the first to give way is the middle branch, vein IVg. 

 This is naturally so, because the cross-vein usually falls away first 

 upon both sides of this branch, where this latter is persistent, while 

 still retaining its tubular shape and active physiological use for the 

 shorter pieces between IV^ and the radius, and IV3 and the cubitus. 

 We see this state of affairs in the Blues and Skippers, where vein 

 IV2 becomes a mere scar. This worn-out vein IV2 speaks for the 

 age of the group. In Hes'peria the short portion between IVj and 

 the radius shows also signs of disintegration, and vein IV^ will 

 undoubtedly in time here share the fate of IVj. Now, in the 

 majority of lepidoptera, the branches of the media do not await this 

 impending fate. They move away and attach themselves to either 

 of the two stationary veins, the radius and cubitus. The movement 

 commences by the upper median branch approaching the radius and 

 the lower the cubitus, keeping up their supply of nutriment from 

 these sources. And this addition to the systems of the radius or 

 cubitus progresses so far that tlie origin and source of the two- 

 branch veins of the media becomes at times obscured. That por- 

 tion of the cross-vein, which formerly lay between these branches 

 and the chief nervure on either side, is transformed into the true 

 continuous base of the branches in their new position. Morpho- 



