336 Mr. A. Radcliffe Grote on the Changes in the 
pterous wing, and the result of this independence has 
been that it has faded out into a scar, as in the second- 
aries of the Skippers. The reason for this disappearance 
lies in the loss of connexion and supply of nutriment 
which it suffers by the reduction and final disappearance 
of the supporting cross-vein, the next step in the disinte- 
gration of the median series. On either side of vein ive 
the supporting cross-vein vanishes and the branch loses 
its power of movement. Meanwhile its companion on 
either side has assured its perpetuity by a union with 
one of the two competing systems of the wing. 
The cross-vein itself finally vanishes. In any event, the 
movement of the middle branch towards either radius or 
cubitus results in a lengthening of the middle portion of 
the cross-vein, and leads to its disintegration. It breaks 
in spots, fading into a functionless scar, sometimes yielding 
at its middle, sometimes near the upper end, so that 
oftenest the sole remnant is a vein-spur representing its 
inferior portion. As the cross-vein thus divides and dis- 
appears, it opens the net-work of the wing longitudinally 
from the base to the outer margin. The wing is thence- 
forth virtually separated into a radial and cubital field, 
the support of the tegument along the middle having 
fallen away. In course of time all scar or trace of the 
former position of the cross-vein vanishes likewise, as in 
the case of the Purple Emperor (Potamis iris). 
I find that that portion of the cross-vein between 
the radius and the upper branch of the media, as well 
as that again between the lower branch and _ the 
cubitus, is retained physiologically as the base of the 
respective vein, upon the disappearance of the middle 
portion of the cross-vein. 
We have mainly followed the fortune of the middle 
branch of the media (vein ive), and have seen that, as it 
attaches itself to either radius or cubitus, this or that 
system is strengthened. This attachment probably has an 
influence upon the mode of flight. The sailing flight of 
Nymphalis or Potamis seems to follow the acquisition of 
vein iva by the radius; the beating or hovering flight 
of Papilio and Sphinx from its conquest by the cubitus. 
But the fortunes of vein iv; are not less interesting 
to follow. In the course of events this vein sometimes 
leaves its position on the cross-vein and creeps along the 
radius, or vein iiis, until its fusion with the latter is 
