22 GROTE—THE DESCENT OF THE PIERIDS. [Jan. 5, 
sionally absent, when the specimen would be referable to A/ancz- 
plum. PP. napi is thus more specialized than P. rape. 
We have thus come somewhat rapidly from local butterflies living 
on the heights of the Andes to the typical genus of the holarctic 
Pierididz. It is clear from the retention of 72 above the discal 
cell, that the ancestors of Phudia have passed through the type of 
Pierts. Trifurcula seemingly represents an intermediate but lateral 
stage, in which 2 is advanced to opposite cross-vein, while JZ2 
has not followed Aft and left the cell. The specializations are 
therefore probably independent and Pua has not passed through 
a Trifurcula stage. 
The genus Pzerzs represents an advanced type of the four-branched 
radius, on the verge of becoming three-branched, but one in which 
the second radial has retained its original position above the cell. 
This type may be used for comparison with the other genera, some 
of which have evidently attained, through convergence, the same 
condition ; while on the passage of the five-branched to the three- 
branched form the stage of Pzerzs is more or less nearly repeated 
in different phyletic lines. For instance, in the ‘‘ Yellows,”’ 
Callidryas represents Pers, with 72 still in position, but it falls 
behind in the long #3. Zerene abandons the original position of 
the second radial, which advances to opposite cross-vein and repeats 
the Zrzfurcula specialization. Lurymus (Colias) goes still further, 
£2 passing beyond the cell and the fork of #3 shortening to nearly 
the condition of Pzeris. Thus we can probably use the type of 
Pieris with advantage to make the position of the other genera 
clearer. 
Although Pua has made an immense stride beyond Pveris 
toward a greater simplification of the neuration, as shown in the 
ascent of the radius by JZ@2, in the short fork of 23-5 with 4/1 
(through which we can imagine that the two may come to fall 
together), yet does Phudia remain on the wveau of Pieris by the 
retained position of Rr and #2. This fact illustrates the in- 
equality of the specialization, in one and the same organ, of the 
characters we use as generic. ‘This is a further amplification of 
that inequality of the specializations between the different stages of 
the insect to which I ventured to draw attention in 1875. It will 
then be impossible to ‘‘reconcile’’ generic groups founded on the 
separate specializations of larva, pupa or imago. Primary, Zz. ¢., 
indifferent characters may be found, by which great groups can be 
