1912] Pupal Wings of Hepialus Thule 243 
fused with another vein to a point opposite the point of separa- 
tion of media and radius. Here the cubitus bends abruptly 
toward the apex of the wing for a short distance and then turns 
abruptly again toward the wing margin, parallel with My. Just 
before reaching the wing margin, it divides into Cu, and Cun. 
The basal part of the cubital trachea of all the front wings 
studied did not lie in the cubital vein but took a short cut 
toward the base of the wing. With the limited material at 
hand it is impossible to determine whether this is a normal 
condition or an artifact due to the mounting. The cubital 
vein cavity and trachea of the hind wing is situated much nearer 
to the medial trachea and vein cavity than in the front wing. 
The cubitus extends parallel to the media until near the wing 
margin where it divides into two branches, Cu; and Cup. 
Medtio-Cubital Cross-Vein.—The medio-cubital cross-vein 
is present, distinct, and in its usual position between M;+, and 
Cu;. This cross-vein differs from the other cross-veins in its 
oblique direction, a direction very suggestive that this was the 
course of the fourth branch of media. The entire lack of trachez 
in these veins defeats such an interpretation. 
Arculus.—The arculus is a cross-vein-like structure at the 
base of the wing extending between radius and cubitus. The 
term arculus was first used for this structure in the wings of 
the Odonata, but as pointed out by Comstock and Needham, it is 
present in the wings of many insects. It is well developed in 
the wings of many Diptera but has not been pointed out hitherto 
in the wings of the Lepidoptera. The arculus, while cross- 
vein-like, is in reality a compound structure. The stem of 
media passes to the base of the wing midway between radius and 
cubitus to the arculus, makes an abrupt bend to the front of 
the wing, forming the anterior portion of the arculus, extends 
to radius, and then makes another abrupt bend and extends to 
the base of the wingin combination with radius. The posterior 
part of the arculus is a true cross-vein, extending from the first 
abrupt bend of media to the cubitus. The anterior or median 
portion of the arculus may be designated as the anterior arculus 
(aa) and the posterior part, consisting of a cross-vein as the 
posterior arculus (pa). 
Both front and hind wings of Hepialus thule show a well 
developed arculus. Practically all of the carefully prepared 
drawings of the wings of the Jugate give some hints as to the 
