14 DRAGONFLIES OF NORTH AMERICA 
The legs are composed, as in other insects, of two short basal joints 
(coxa and trochanter), that make the upward turn from beneath the 
body; two long joints (femur and tbia), that meet at the knees; and 
three short joints and a pair of claws that together form the foot 
(tarsus). In dragonfly legs there is great variation in size, length and 
development of the spines. Generally speaking, each femur and each 
tibia has a‘double row of spines, one on the anterior and one on the 
posterior aspect, beneath. The spines increase in size and number from 
the front to the hind legs, and are inclined toward the tarsi. These 
spines, which at first glance might appear to be intended as weapons, 
seem to have developed for employment of the legs as a food trap. 
It is perfectly easy to understand how the “‘leg basket” operates, but 
extremely difficult actually to observe the process, because of the 
lightning-like swiftness of the dragonfly’s movements. Kellogg (’05) 
says of it: ‘‘When the prey is come up with, however, it is caught, not 
by the mouth but by the ‘leg basket.’ The thorax is so modified and 
the insertion of the legs is such, that all the legs are brought close 
together and far forward so that they can be clasped together like six 
slender, spiny, grasping arms just below the head. Although the 
catching and eating is all done in the air and very quickly, observers 
have been able to see that the prey is caught in this ‘leg basket’ and 
then held in the fore legs while being bitten and devoured.” 
The spines on the anterior sides of the fore tibia show an interesting 
modification which is doubtless for holding the food. Instead of a 
regular series of long spines such as are found upon the tibiae of the 
second and third pair of legs, the inferior third of the first tibia bears a 
series of small spines very numerous and closely set, so as to form a sort 
of comb. This comb no doubt enables the dragonfly to hold very 
firmly the small insects which compose his bill-of-fare. 
Venation—The. wings are always well developed. Certain wing 
structures demand particular attention. 
Nothing will be more useful to one who is trying to learn the dragon- 
flies than a little knowledge of the venation. Vein characters are very 
definite. Theyare plain as the printed page. Nearlyall the genera may 
be recognized from the venation of their wings alone. If at the first 
glance their rich network appears complicated, half an hour’s study 
of the following diagrams and comparison of them with real wings 
should enable one to master details sufficient for all purposes of this 
book. . 
The principal veins are the same as in other insects. In our figures 
they bear the following names and designations: 
