MORPHOLOGY OF THE ALEYRODn)iE. 9 



sacs. During the pupal stage the wing disks come to lie outside the 

 body, the pads are developed, and in the late pupae the wings them- 

 selves are folded up within the case. They are four in number, 

 membranous, and are composed of two thin, superimposed lamellae. 

 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 forcwing 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 haii-s 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 Aphidida^ 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. ^* Comparing with this the wings of Udaraoselis pig- 

 mentaria Enderlein (PI. I, fig. •!), 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 ^ 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 

 l)syllid, 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 Udamoselina^ has been erected 

 and at present includes only the one Icnown form. 



In the genus Aleurodlcus (PI. 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 j, radial sector, and media, are represented as they are 

 in Udamoselis. Tlie 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 Aleurodicina? may be erected. It is 



