434 



flattened. The comb (tic) formed by these closely placed setae is 

 probably used for cleansing the mouth-parts or the antennae. There 

 is a great deal of variation in the length of the tibial setae and also in 

 the number present in different subfamilies. 



Tarsi. — The tarsi are always composed of three segments, the seg- 

 ments increasing in length from the proximal to the distal end (Fig. 

 35, ta). They are also provided with a double row of setae beneath, 

 but these are never as long as the tibial or femoral setae. 



Pretarsiis. — The pretarsus (Fig. 19, pta) is beyond the end of the 

 third tarsal segment and consists of a small shield-shaped piece on the 

 ventral surface just beneath the bases of the claws. It extends back 

 into the third segment, and in order to be seen best the claws should be 

 pulled outward a little. There is also a small projection attached to the 

 tip of this sclerite, but this is not homologous with the empodium of 

 other insects. The ventral apical margin of the last segment of the 

 tarsus is deeply emarginate on each side of the pretarsus. 



Claws. — The claws are long and slender and the tips are always 

 notched or bifid (Fig. 35, cw). The rays are seldom equal in length, 

 and in some species the notch is far proximad of the apex. 



Wings (Figs. 73, 74, 78, 81-90). — All Zygoptera have four sim- 

 ilar membranous wings. In respect to venation and shape, the genus 

 Hetaerina may be said to have the most primitive wing of any zygop- 

 teron found in Illinois (Figs. 74, 78). The position and course of 

 the veins in the wings of this genus are as follows : — The costa, first 

 longitudinal vein, forms the cephalic margin of the wing. The sub- 

 costa, second longitudinal vein, extends half the length of the wing 

 from the base and ends abruptly in a short fork which marks an in- 

 dentation in the margin. The two forks of the tip of this vein are 

 in line with a heavy cross-vein caudad of it, and the brace formed by 

 the alignment of the cross-vein and the subcostal forks is known as the 

 nodus. The third longitudinal vein extends from base to apex of the 

 wing and is composed of fused radius (R) and media (M) as far 

 distad as the nodus and first radius (Ri) plus the second subcosta 

 from nodus to apex. There are a number of cross-veins extending 

 between costa and subcosta from the base of the wang to the nodus — 

 the antenodal cross-veins. Between costa and radius, distad of the 

 nodus and proximad of the stigma — the heavily chitinized spot near 

 the apex of the wing — are the postnodal cross-veins. The remaining 

 branches of the radius are united, forming the radial sector (Rs), and 

 separate from the main trunk at the nodus. The course of the radial 

 sector is difficult to follow because of its crossing one or two of the 

 median veins. In Hetaerina the radial sector branches from the radius 



