GENERIC CLASSIFICATION OF APHIDIDAE. 63 
the process of degeneration and only two ovaries, one on each side, develop. Of these 
one finally degenerates and the egg of the other grows until it fills almost the entire 
body and the insect appears to be little else than egg. 1 
It will be seen at a glance that such a method of egg development 
is entirely different from that met with in members of the genera which 
have been heretofore placed in the subfamily. The Hormaphidini and 
the Thelaxini, as will be seen under the discussion of those tribes, 
have sexual females which develop normal ovaries and lay several 
eggs in the same way as do the Aphidini, Lachnini, and other groups. 
It is true that some have developed gall formation and highly special- 
ized, wax-secreting organs, but this is more of a parallelism than a 
close relationship, as is indicated by the sexual forms. The wax- 
secreting organs of the Eriosomatinae vary considerably in structure. 
A study of those in the genus Eriosoma has been presented by the 
writer (1915). The glands here are compound, each cell containing a 
central wax chamber into which the wax is secreted and from which 
it is forced out as a fine waxen thread. In other genera the wax 
glands take on the nature of plates, illustrated in the genus 
Prociphilus. These -glands are essentially the same in general struc- 
ture as are those in Eriosoma, but the wax cells are placed very 
close together and are so extremely elongate that their openings to the 
surface are very small. A large number of these gives the appearance 
of a more or less uniform plate. The structure, however, in the two 
genera follows the same lines. 
The wing venation in this subfamily presents as great a reduction 
as in any of the subfamilies of the Aphididae and in this respect it is 
comparable to the Hormaphidinae. In the fore wings the reduction 
is shown in the media which is never branched more than once. Dr. 
Patch has pointed out the homologies of the veins and has indicated 
that in all of these cases the branches represent M 1+2 and M 3+4 . 
In some cases, however, it would appear as if they were Mj and M 4 . 
In other genera the media is indicated as a single vein. The radial 
sector is in nearly every case present and the cubitus and first anal 
are prominent veins. The tracheae are figured for the subfamily 
under the genus Eriosoma. In the hind wings the radial sector is 
always present and two oblique veins are nearly always found. 
These are the media and the cubitus. In several genera, however, 
the cubitus has disappeared and only the media remains as the one 
transverse vein in the hind wings. 
The cornicles in the genera of this subfamily are not prominently 
developed. Indeed, they are absent altogether in certain of the 
tribes. In the genus Eriosoma they are chitinized rings slightly 
elevated on shallow hairy cones. The opening of the cornicles is 
closed by a muscle and from the cornicle a narrow duct leads to a 
i Baker, A. C. The woolly apple aphis. U. S. Dept. Agr., Off. of Sec, Kept. 101, p. 43. 1915. 
