MORPHOLOGY OF THE ALEYRODID^. 9 
sacs. During the pupal stage the wing disks come to lie outside the 
body, the pads are developed, and in the late pupa? the wings them- 
selves are folded up within the case. They are four in number, 
membranous, and are composed of two thin, superimposed lamella?. 
In the preparation of mounts with potassium hydroxid, these plates 
often become separated and the wings become opaque and sac : like in 
form. The border of the wings all around in most species is covered 
with a series of knob-like or bead-like projections on which occur a 
number of fine hairs. These hairs vary in number. In some species 
there is a large central hair on each knob with two or three small 
ones on each side. In others the hairs are subequal in length and 
very minute. In Aleurodiciis the proximal half of the costal margin 
cf the forewing is armed with a number of large spine-like hairs 
situated on small receptacles. These hairs are placed a short dis- 
tance in from the costal margin and are arranged along what ap- 
parently represents the subcosta. The hairs are directed distad. 
The hind wing of all species is armed on the proximal portion of 
its costal margin with a row of strong curved hairs which aid in 
keeping the wings together during flight. The number of these 
hairs varies, but from seven to nine hairs are most usually met with. 
In the Psyllidse a similar row of hairs is situated in the same region, 
but there is usually a larger number. In the Aphididse, on the other 
hand, this structure is usually replaced by three hook-like hairs situ- 
ated, not at the base, but on the distal half of the wing. 
To illustrate the venation in this family we will use as a basis of 
comparison the wing of a species of the psyllid genus Trioza (PL I, 
fig. 2), following the nomenclature as worked out for that genus by 
Miss Patch. 14 Comparing with this the wings of Udamoselis pig- 
mentaria Enderlein (PI. I, fig. 4), we see that the veins of the costal 
region are separate, although very close. These undoubtedly repre- 
sent the costa «and subcosta. We find that radius x and the radial 
sector are represented in exactly the same manner as in Trioza. The 
media and cubitus have a position very similar to these veins in the 
psyllid, but are not branched, while the first anal, the only one pres- 
ent, is in identically the same position in both forms. For species 
possessing these veins the subfamily Udamoselinse has been erected 
and at present includes only the one known form. 
In the genus Aleurodicus (PL I, fig. 7) the costal vein is made up 
of costa and subcosta. These are as a rule united, but in some species 
they are separated at the base and can be distinctly traced. The 
veins radius „ radial sector, and media, are represented as they are 
in Udamoselis. The cubitus and anal, however, have disappeared. 
This disappearance of the cubitus and the retention of the media 
form one of the main lines of descent in the family and for the 
forms showing it the subfamily Aleurodicinse may be erected. It is 
