1900. ] GROTE—THE DESCENT OF THE PIERIDS. 58 
Phulia and Pseudopontia does the second median branchlet follow 
this example. Meanwhile the third median attaches itself to the 
cubital system. In the Pieridide, the movement, by which the 
median system seeks its extirpation, is arrested at this point; the 
cell never completely opening, although often degenerate, between 
M2 and M3, as in certain WMymphaline, in which, per contra, the 
upper two branchlets of the media never leave the cross-vein, 
crowding themselves into the upper corner, but refusing to ascend 
the radius. This is the general attitude of the brush-footed butter- 
flies. The opening of the cell, wherever this happens by the disap- 
pearance of the cross-vein centrally, is the signal that the median 
system has finally departed ; the radial and cubital systems of the 
wing inheriting its last possessions, the three terminal branchlets 
which they divide between them and subsequently have to feed. The 
base of the media had departed long ago ; the veins running from 
the cross-vein to the root of the wing are now only found in the 
Tineides, although scars along the tegument of the cell and little 
backward jutting spurs on the cross-vein tell of their former exist- 
ence in the Pierids as well. The movements of the veins belonging 
to the two systems are unequal. 
The hind wings seem to show little movement of the veins; they 
have performed an antecedent work in the simplification of the 
radius, which shows asa single vein. The first radial branch has 
seemingly gone to make up the humeral cell, but in the Pierids, the 
humeral cell has itself become absorbed and all traces of the forking 
of the radius at base have vanished. I therefore notate the radius 
by a simple ,; theoretically it should stand R2 + 3+ 4+ 5, 
while the subcostal vein should stand Sc. + A1, marking where 
the radial branchlets have respectively disappeared to. The hind 
wings of the Nymphalids show a greater movement of the veins 
than those of the Pierids ; in the brush-footed butterflies the disin- 
tegration of the median series seems here to find its impulse and the 
specialization of the hind wings is in a constant state of advance. 
This is seen by the opening of the cell on the secondaries of 
Araschnia, Melitea, etc., while the cell on primaries remains still 
more or less perfectly closed. Evolution is more active with the 
fore wings of the Pierids, with the hind wings of the Nymphalids ; 
in which latter the bunching of the median nervules at the upper 
corner of the cell seems to meet the requirements of their mode of 
flight. 
