1906] 
WILLISTON— DIPTEROUS WING 
155 
only. The hind branch of the fifth is the one which Loew called the ‘posterior 
basal cross-vein’, but in this I^ocw was very clearly wrong; this hind branch is not a 
cross-vein in any sense of the word, and few writers have made use of the term since 
his time. The vein closing the anal cell in the higher diptera should be known as 
the ‘posterior branch of the fifth vein.’ The anterior branch of this vein is the one 
bounding the fitfh posterior cell, when ])re.sent, in front, and is always present as a 
discrete vein in those wings having a (fiscal cell in the vein separating the last poste- 
rior cell from the second basal cell. The two branches of this vein are consjiicuously 
evident of course in many of the Nemocera without (fiscal cell. Comstock, agreeing 
with Schiner, believes that the fourth vein (Vein V) is primitively three-branched, 
the ])roximal branch enclosing the (fiscal cell, and, in nearly all cases he assumes 
that when but a single branch of the fourth vein is ])resent it is the ])roximal one; 
a belief with which I do not at all agree. It is a singular fact that no dipteron, 
(unless it be Lonchoptera) presents a simple three-branched fourth vein unconnect(Hl 
with the fifth, and I am myself inclined to the belief that it is the fifth vein which is 
normally three-branched and not the fourth; and that the (fiscal cell, when present, 
is not due to the proximal branching, but rather to the ])resence of a true cross-vein 
separating the .second basal from the (fiscal cell. I of cour.se have not had the opj)or- 
tunity to study the venation of other orders of insects as had Comstock and Needham, 
but so far as my studies go, I find no conclusive evidence in them. If the fourth 
vein is three branched and discal cell ])resent, the vein sej)arating the discal from the 
second basal is of course the first section of the [)roximal branch of the fourth vein; 
if the fifth vein is really the one that is three-branched, then this vein, at the outer 
end of the .second basal, is always a true cro.ss-vein, which it always is in the Com- 
stock system when the discal cell is absent. Schiner it was who, very strangely for 
so acute an observer, gave to the short vein at the outer end of the second basal cell 
in the nemocera the name of posterior or great cro.ss-vein, and Osten Sacken, perhaps 
led astray* by his authority at a time when he had not given much thought to the 
brachycerous di|5tera, applied to the first section of the anterior branch of the fifth 
the name of ‘great cros.s-vein’ in the Tipulidae. The name ‘posterior’ or ‘great’ 
cross-vein is a])plied to the cross-vein closing the discal cell outwardly in all the muscid 
flies. Now it is very evident that the ab.sence of a discal cell, in the mosquitoes for 
instance, is not due to the coalescence of the (fiscal and .second basal cells, but to the 
absence of the ‘posterior cros.s-vein’ of the muscid and brachycerous flies, and the 
application of this name to the vein at the inner end of the (fiscal cell is very ch'arly 
incongruous. My attention to this incongruity was first fixed by the common usage 
among students of the Culicidae in calling the vein at the outer end of the .second 
