162 PHILIP p. CALVERT. 



tibia may be much longer (Aeschna, Libellula). When the spines 

 of both tibial rows are fairly similar in shape, those of the anterior 

 row may be more numerous on the first legs and less numerous on 

 the second and third (Calopteryz, Lestes, Libelhda), or more numer- 

 ous on the first and third and of equal number on the second legs 

 (females of Corduleg aster). On the other hand the spines of the 

 anterior row may be replaced by knobs on the second and third tibia? 

 (most males of Cordulegaster), or on all the tibise (males of Cordule- 

 gaster diastatops). The number of tibial spines, and the i-elation 

 existing between their length and the intervals separating them, have 

 yielded generic characters in the Agrioninse and Libellulinse. When 

 the femoral spines are shorter than those of the tibia, each of the 

 two primary rows may become a double or a triple row {Cordule- 

 gader). Moreover, superior longitudinal rows of spines may be 

 developed on the femur {Aeschna), or on the tibia {Gomphus). The 

 tarsus consists of three joints, increasing in length distally in all 

 living Odonata ; the fossil Calopterygine Tarsophlebia has the basal 

 joint as long as the second and third joints together. Each joint 

 bears two rows of spines, continuations of those on the tibia. The 

 terminal joint bears a pair of acute, divergent, tarsal nails, each of 

 which has usually an acute tooth on the lower side ; the position of 

 this tooth varies in different groups. A minute process occurs be- 

 tween the two nails at their bases. 



After remarking the apparently disproportionate size of the legs 

 in an insect which uses them so little for locomotion, McLachlan 

 suggests that " the greatest service all the legs render is possibly in 

 enabling the creature to rest lightly so that it can quit a position of 

 repose in chase of passing prey in the quickest possible manner." 

 (Encyc. Brit. 9th ed. art. Dragonfly). The first pair of legs are 

 usually employed to hold the food as it is devoured. 



The icmgs are prolongations of the integument of the meso- and 

 metathorax between the tergum and pleuron. Of the two laminre 

 of which they are formed, the up{)er is tergal, the lower pleural. 

 The wings are large, membranous and many-veined. The front 

 wings are usually about one millimetre longer than the hind wings ; 

 the latter are of equal width with the former at the base, in the 

 Zygoptera, but distinctly wider in the Anisoptera. The arrangement 

 of the veins offers many characters for classification, as well as af- 

 fording a means for exactly locating wing-markings. Inasmuch as 

 the homologies of the veins in different orders of Insects have not 



