421 



capable of being telescoped into the coxa. The second segment is 

 longer, and its ventral length is greater than its dorsal. The femora 

 are subequal in length, the posterior being slightly longer, especially 

 in Argia and the Lestinae. The tibiae are also nearly equal in length 

 and are slender and cylindrical. The tarsi have three segments. The 

 proximal segment is short and is extended below the second segment 

 so that its ventral length is greater than its dorsal. The second segment 

 is usually about twice the length of the proximal but, like the proximal 

 one, is extended on the ventral side. The third segment is longer 

 than either of the two proximal ones, being in some cases nearly 

 twice as long as the second and four times as long as the first. At the 

 distal end of the third segment, on the ventral surface, there can be 

 found a small sclerite which probably represents an extra tarsal seg- 

 ment and is known as the pretarsus (Fig. 19, pta). It is drawn out 

 distally into a slender process. The tarsal claws vary to some extent 

 in length but are always sharply pointed and somewhat swollen at base. 

 They are never bifid at the tip as in the adult. The legs of the nymphs 

 never bear the long spines characteristic of the adult but, instead, there 

 are weak setae or short spinules which collect particles of dirt and 

 enable the insect to hide with ease. In the Agrioninae, there are to 

 be found short, minute, three-pointed scales at the ends of the tibiae, 

 the function of which is obscure (Fig. 19). The tarsi in all species 

 possess two to four rows of short setae on the ventral surface. The 

 markings of the legs vary with the genus, but consist largely of black 

 rings on the femora and tibiae. In Agrion, nearly the whole of the 

 femur is dark except a whitish ring near the apex. The tibial bands 

 are mostly restricted to the proximal third and are lacking in most 

 species. 



Wing-cases. — The wing-cases of Zygoptera appear early and at 

 the completion of nymphal life usually extend as far caudad as the 

 fifth or sixth abdominal segment (Fig. 25, wc). The tracheation of 

 the pad is often obscure but the veins are sometimes plain enough to be 

 of value in identification. Ontogenetic studies of the wings can only 

 be made at intervals during the growth of the nymph, the obscure 

 nature of the contents of the pad making such study difficult during the 

 greater part of the time. In no case do we find the radial sector actu- 

 ally crossing over the media as in the Anisoptera, and, as pointed out 

 by Needham ('03), the subnodal cross-vein formed by the proximal 

 end of the radial sector has been reduced and lost. The distal portion, 

 however, may be seen in Lestes, but not usually in other species, and 

 branches from the second media a short distance from its separation 

 from the first media (Fig. 14, Rs). 



