No. 382.] THE WINGS OF INSECTS. 775 
kinds: first, the development of accessory veins; second, the 
modification of the primitive veins so that they are no longer 
dichotomously branched. The former has been discussed 
above ; we will now briefly refer to the latter. For this pur- 
pose we will give a series of diagrams illustrating several types 
of branching of the radial sector. 
Fig. 58a represents the typical or dichotomously branched 
radial sector. Fig. 58% represents a typical radial sector with 
the addition of some 
accessory veins on the q- ie 
caudal side of vein Re. 5 
Such a radial sector oc- R, 
curs in the fore wing of is R 
Ithone! In this case 9 R 
the radial sector is 
nearly pectinate, but not R, 
quite so, owing to the 5 
forked condition of vein „ ‘ 
R 4+5. In Chauliodes. ¢ R, 
(Figs. 53, 58c) veins 
R4 and Rs coalesce to 
the margin of the wing; 
and in this way the pec- 
tinate type is attained. 
In Hemerobius (Figs. 
58d, 59) the pectinate 
type has been attained 
by fission instead of 
coalescence. Here veins =k 
R4 and Rs have split © ee 
apart till vein R; arises f 
from the main stem of 
radius. R 
a 
When many cross- Fic. 58. — Diagrams of several types of radius. 
veins are present, the : 
dichotomy of the branching of the sector may be suppressed in 
still another way, by the transference of the base of vein 4 to 
1 Brongniart. Rech. sur I Hist. d. Insectes Fossiles, Pl. I, Fig. 10. 
