222 NEW YORK STATE MUSEUM 



not well arranged to serve the purposes of flight. A comparison 

 of the generahzed members of the family with the more speciahzed, 

 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. ii] 

 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. 



