OZ GROTE—THE DESCENT OF THE PIERIDS. [Jan. 5, 
have abstained from interfering in the question of the necessity 
for generic titles. 
MOVEMENT OF THE VEINS IN THE WINGS OF THE PIERIDIDA. 
The movable veins of the primary wing are the branchlets of the 
radius and media. The generalized type has five branchlets to the 
radius, two arising above the discal cell, the remainder beyond the 
cross-vein. ‘The diminution by specialization of the branchlets is 
effected by their outward movement, and they appear to pass off by 
the external margin of the wing. It is especially the movement of 
the second radial branchlet which gives rise to interesting combi- 
nations. Sometimes the outer branchlets disappear, leaving a 
single vein, and the second radial remains still in position, as in 
Pontia. Again the second radial commences its travels along the 
upper side of the vein, stopping at various points along the route, 
before the terminal branchlets have been disposed of, as in Aztho- 
charis. Arrived at the point opposite the cross-vein, it gives the 
Trifurcula position, as I have called it in this paper, in which the 
second radial, then the main vein of the radius from which it 
ascends, and finally the cross-vein, running in an opposed down- 
ward direction, meeting, give the appearance of a trident. This 
position of R2 is not confined to 772furcula ; it always recurs and 
must recur in the progress of the second radial branchlet along the 
vein, and in fact is exhibited now by a number of genera. Also in 
genera, like Piccarda, Delias, Perrhybris, in which the second 
radial has long passed the cross-vein by, the ancestors must have 
exhibited the Z7zfurcu/a position at some time in their history, 
when their second radial branchlet attained this point, and for the 
moment retained it. In the Pieridide the first radial always keeps 
its position above the cell. 
The generalized type, so far as the media is concerned, has the 
three branchlets all springing from the cross-vein, the second 
medial having a central position. This is soon abandoned in spe- 
cialization and the branchlet approaches the radius, while the cross- 
vein, in the widening space between J/2 and 473, become some- 
what worn, the first sign of the ultimate breaking up of the median 
system through the opening of the discal cell. In the meantime the 
first median branchlet leaves the cross-vein and ascends the radius 
on its lower side. Only in such extreme cases of specialization as 
