222 NEW YORK STATE MUSEUM 
not well arranged to serve the purposes of flight. A comparison 
of the generalized members of the family with the more specialized, 
gives unmistakable evidence as to this, and a comparison of the 
Diptera as a whole but adds further confirmation. The best flyers 
have fewer veins, and have them arranged in such a manner to 
better brace the wing membrane. 
The course of primitive veins was probably one of gentle diverg- 
ence out from the narrow base across the wing disk. ‘Their fork- 
ing was dichotomous; in all wings there still inhere some traces 
of this original dichotomy, that is due to the first formation of 
veins about primeval tracheae. When elimination of cross veins 
occurred, those cross veins would be preserved that occupied ad- 
vantageous position joining the nearest points of adjacent veins. 
For the wing is a machine, and one of immense importance to its 
possessor, and its efficiency would count for much in the struggle 
for existence. That efficiency could depend on nothing else than 
advantageous arrangement of its constituent parts. 
The wing is moved up and down by muscles within the thorax 
attached to its basal parts; its front margin is rigid, by reason of © 
the strength. and close approximation of the three veins there and 
the gutterlike depression of the membrane they maintain between 
them, their close union with the basal hinge apparatus, and their 
junction at the humeral cross vein and by means of the tip of the 
subcosta. At the tip of the subcosta lies the stigma —a weighted 
striking point, strongly, though often diffusely chitinized. This is 
the point of greatest impact against the air. The part beyond the 
stigma and the whole outer and hinder border are flexible; and 
forward progression through the air depends upon the sculling 
action which this combination of rigid front margin and pliant 
hinder part secures. 
The wing has been called not inaptly “a sort of flexible sail;” 
and if we scan any Tipulid wing (excepting possibly a few of the 
most generalized) we may readily see that the strong main stem 
of the radial vein stands in the place of the main mast, [fig. 11] 
and the strong cubital vein, in the place of the boom that keeps 
the sail full spread. From an imaginary mast head in the region 
of the stigma a sort of “ bolt cord” is formed out of cross veins 
and divaricated forks, joining together in secure but flexible union 
the outer ends of mast and boom. Moreover, as were befitting in 
a sail, the base of the main mast is rigid, while the base of the 
boom is flexibly slung. 
