288 SMITHSONIAN MISCELLANEOUS COLLECTIONS [voL. 48 
exactly the line which, in the adult wing, will be occupied by the 
structures just described (pl. L1x, 1). These spurs surely represent 
a once well-developed vein which in the course of phylogeny has 
almost disappeared. As might be expected from the fact that they 
are vestiges of a disappearing structure, these traces vary in degree 
of preservation from a strong well-marked condition to total absence. 
It is comparatively rare to find the line and both spurs well preserved 
in the same wing; usually one or more of these vestiges has been 
lost. The spur at the outer end of the cell is not always on M, but 
in many cases rests on radius, as in Semnopsyche diana (plate fig. 
13). It is not always an easy matter to see these traces, even in 
cleared and mounted wings where they are present, but in photo- 
graphs, where all structures are magnified, their presence can readily 
be detected. There are, however, numerous examples in which such 
vestiges are visible in the unbleached and unmounted wing, as in 
certain species of the larger Papilios (pl. L1x, 2). The variation in 
the position of the spur lying nearer the outer end of the discal 
cell is significant of different courses of phylogenetic development. 
These I shall attempt to trace in the following paragraphs. 
In many wings, such as those of Anosia plexippus and Apostraphia 
charithonia, this spur is located on the base of M,; in others, of which 
Semnopsyche diana is typical, it occurs on radius just before the end 
of the discal cell; and in still other cases, such as Diethria clymena, 
it lies on radius proximad of the origin of R, (pls. Lx, LX, figs. 
12-15). All stages from the condition in Anosia to that in Diethria 
have been found. 
The position of the spur on the base of M, is due to a complete 
coalescence of R,,; with the radio-medial cross-vein and, following 
that, a short coalescence with M/,. While this process has resulted in 
the real obliteration of the radio-medial cross-vein, it has produced 
an apparent cross-vein between M, and FR; for, when the basal part 
of R,,; has atophied, nothing but a more or less well-marked stump 
is left on M, to explain that this apparent cross-vein is none other 
than the stem F,,, passing over to coalesce for a distance with R 
before reaching the outer edge of the wing. This apparent cross- 
vein differs in direction from the real cross-vein. The former extends 
obliquely from M, toward the apex of the wing, while the latter 
extends obliquely from R toward the outer hind corner (plate figs. 
14 and 15). . The first type is almost characteristic of the Neotro- 
pide, Danaidz, Heliconidz, and Libytheidz, and the second occurs 
very generally in the Nymphalidz, Satyride, Morphide, Brassolide, 
and Acreide. 
