HEADLEE] A STUDY IN BUTTERFLY WING-VENATION 291 
I have cited only a few of the examples available and, while they 
show how widely this modification is scattered through the groups, 
they show nothing of its prevalence among the members of the 
individual families, and consequently nothing very conclusive as to 
its history and significance. In order to get light on this point I 
carefully examined the mounted and photographed wings of 171 
species, representing 158 genera and 16 families of Rhopalocera. 
These wings were taken from specimens representing all the life 
zones of the world, a majority being secured from North, Central, 
and South America. This latter fact does not impair the universal 
nature of the evidence for South America alone, according to Staud- 
inger and Schatz (’85),1 possesses 272 genera represented by 4,500 
species, or about one-half of all the butterflies then known. All my 
specimens of the following families show traces of a split-back condi- 
tion of R,,,: four genera of the Papilionide; one genus of the 
Parnasside; one genus of the Danaide; fourteen genera of the 
Neotropide; three genera of the Heliconide; one genus of the 
Libytheide; two genera of the Brassolidz; one genus of the Mor- 
phide. In the following families the relative number which show 
distinct traces of this modification is indicated by per cent: 89 per 
cent. for forty-one genera of the Nymphalide; 80 per cent. of 
fifteen genera of the Satyride; 76 per cent. of eight genera of the 
Hesperide; 70 per cent. of twenty genera of the Pieride; 50 per 
cent. of one genus, represented by two species, of the Acreide; 14 
per cent. of seven genera of the Erycinidz; 7 per cent. of twenty- 
seven genera of the Lycenidz. Thus in eight families all specimens 
and in five 50 per cent. or more show traces of this modification of 
radius, while in only two does the per cent. fall below fifty. These 
facts serve to show ‘that this modification of radius is exceedingly 
prevalent and, to the student of rhopalocerous wings, also that, in 
general, it prevails most completely in those wings which have 
experienced the least reduction of other veins and are, in fact, the 
most generalized. 
The wide distribution of this modification of radius and the fact 
that it is best preserved in generalized wings, can best be accounted 
for by the supposition that radius of the progenitors of the present 
butterflies was characterized by a split-back condition of R,,;. This 
character has arisen, reached its maximum development, and is now 
reduced to mere vestiges, even these having almost disappeared in 
some families. 
10. Staudinger and E. Schatz, Exotische Schmetterlinge, II Theil, 1885, 
p. 28. 
