REPORT OF THE STATE ENTOMOLOGISP 1907 228 
But this analogy might easily be carried too far. For the wing 
is nota sail, to belly with the wind and hold against its pressure, | 
but it is a flexible scull, to be swung rapidly against still air, up and 
down, rigid in front, yielding behind, giving a resultant in forward 
motion of both strokes rapidly repeated. Hence beyond the bolt 
cord that may be discerned in the line of cross veins and forks, 
and behind the boom that the stem of the cubital vein represents, 
there is a wide border that has no counterpart in a sail. Further- 
more, the analogy will be misleading if held too rigidly even for 
the inner triangular area. For the “bolt cord” is often not con- 
tinuous to vein R! but stops at the radial sector,’ and it is cut by 
one Or more furrows, that greatly increase its flexibility? 
The analogy will have served its purpose if it fixes our attention 
upon the triangular outlines of the supporting framework of the 
wing, for it will abundantly appear in the following pages that 
along these lines of support have played the forces that have 
evolved the Tipulid wing. 
This general arrangement of parts is not peculiar to Tipulidae, 
nor even to Diptera, but is characteristic of the vast majority of 
winged insects. It seems strange that so little attention should 
have been paid to 
ie Ione «ONT 
5 ie, | — 
= See. . students of vena- 
SS iom, I Gesiire ito 
ba ae tee 
emphasize it here 
by means of the 
accompanying dia- 
NS 3S gram: [fig. 13] in. 
which the arrows indicate the outer line of transverse joinings. 
For this I think it would be convenient to use the simple and sug- 
gestive term cord. ‘The shaded mainmast strip at the front is the 
costo-subcosto-radial combination. The posterior boundary of 
the larger triangle is the cubitus, and of the lesser included tri- 
angle, the radial sector. 
*Thus making, however, a trapezoidal, instead of a triangular sail area. 
2 These furrows allow the wing to close somewhat on the up stroke, and 
are doubtless a compensation for the pull of gravity on the heavy body 
of a crane fly. They are best developed in the Tipulinae with the heaviest 
bodies (Holorusia, etc.). One can see how they work by holding a fresh 
or a softened wing firmly by its base and blowing air alternately against its 
upper and lower surfaces through a bent tube while looking horizontally at 
its tip. The anal furrow (behind Cu) allows almost complete flexion on the 
up stroke. On the down stroke the whole wing tends to flatten out. 
