224 ‘ NEW YORK STATE MUSEUM 
The main phenomena of specialization of wings of crane flies 
Hakenunnec: 
I The bringing into line for mutual support of cross veins and 
adjacent forks. This may be soon understood by comparing figures. 
12 and 13, or by comparing any specialized crane fly wing with the 
wing of Macrochile [pl. 14, fig. 1]. 
2 The reduction of superfluous veins and cross veins. 
3 The differentiation between the veins that remain. . 
The last two processes are really one; for both are at bottom 
and redistribution of the strength-giving material of the wing. 
When but one cross vein is left where two were before, that one 
is larger and stronger. This may be perhaps regarded as hypo- 
thetical, but the converse of it is not, for two cross veins occasion- 
ally appear adventitiously, where normally there is one (as, for 
example, cross vein m in Acyphona) and then they are always 
markedly weaker than the single one would be. The differentia- 
tion between. longitudinal veins consists likewise essentially in 
putting the strength-giving material where it will do the most good. 
That differentiation is but little exaggerated in figure 13. Witness 
the photographs of plates 11 to 13. Strong and: weak stems alter- 
nate Radius is strong and media weak, cubitus is strong and the 
first anal weak, the second anal is stronger than the first, and the 
third is usually absent altogether. 
Our knowledge of the mechanics of insects is yet caceeinels 
meager and unsatisfactory. It is sufficient to be suggestive how- 
ever of possible reasons underlying the main phenomena of their 
specialization. . 
Elements of the venation individually considered 
It will be advantageous now to consider the parts of the venation 
severally, looking first at the veins, then at the cross veins, and 
then at their mutual behavior and adjustment. , 
Longitudinal veins. The costa is always simple, and forms 
the front border of the wing. 
The subcosta is a weaker vein that lies in the bottom of the 
furrow of the fore border between costa and radius. It is bound 
to radius by a basal fusion and to costa by the humeral cross veins: 
17 have noted a similar differentiation under very different vein arrange- 
ment in the Odonata [U. S. Nat. Mus. Proc. 1903. 26:737], and have stated 
the conclusion thus: ‘The strong vein bounds posteriorly the area in 
which the weaker one lies.” 
