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IOWA ACADEMY OF SCIENCE 
veins, the third of which is again branched. This thickened vein is composed of 
the subcostal, the radial, except the radial sector, the basal portion of the 
medial, and cubital veins. The first and second apparent branches are the sec- 
ond and first branches of the cubital vein respectively. The third apparent 
branch is the medial with its three branches. The fourth apparent branch is 
the radial sector. The anal vein in the adult wing remains as only a fold at 
the base of the second cubital vein and forms a thickening for the attachment of 
the hooks of the caudal wing. 
As specialization progresses in the other subfamilies of the Aphididae a re- 
duction of the medial vein takes place and there is first a disappearance of the 
branches of this vein and, in the most specialized wing, a complete disappear- 
ance of the vein itself. In the subfamily Schizoneurinae (fig. 5) the further 
specialization is by the coalescence of branches, one and two, of the medial 
vein which leaves this vein but two branched. In other respects the venation 
remains practically the same as in the most generalized wing. 
In the subfamily Pemphiginae (fig. 6) the specialization has been carried still 
further by the coalescence of all the branches of the medial vein into a simple 
vein. 
In the most specialized Aphid, such as is found in the subfamily Cherma- 
phinae (fig. 7), all trace of the medial vein is lost. There are three ways in 
which it may have disappeared. It may have coalesced with the subcostal and 
radial veins. It may have been suppressed early in its development. It may 
have coalesced with the cubital vein. The coalescence of the medial vein with 
the subcostal and radial veins is quite doubtful as the radial sector in the wings 
of this subfamily still retains its relationship to the radial and subcostal veins 
as in the other subfamilies. The entire suppression of the medial vein is also 
quite doubtful for, while, in some of the less specialized Aphid wings there are 
apparent partial suppressions of this vein, such a suppression would be unusual. 
Wing veins do not entirely disappear in this manner. The union of the medial 
vein with the cubital vein I am inclined to consider as the most plausible for, 
in many of the more specialized wings, there is a reduction in the area be- 
tween the medial and cubital veins. There is also a partial coalescence” of the 
medial and branch one of the cubital in the more generalized wing as is shown 
in (fig. 4a). This partial coalescence has probably been completed in the Cher- 
maphinae, and the medial and branch one of the cubital are apparently a 
single vein. 
The study of the hind wings is more difficult than the fore wings, as they are 
too small and delicate to obtain mounts of. It is quite probable, however, that 
the condition that exists here is the same as that in the Chermaphinae, except 
that the radical sector has been lost by coalescence with the subcostal and 
radial veins. In the hind wing of the Chermaphinae all the veins have coalesced 
into one single longitudinal vein. 
The following table gives the relation between the general and the arbitrary 
nomenclature : 
