Stough: the hackberry psylla. I4d 



LEGS. 



The prothoracic and mesothoracic legs are essentially the 

 same in structure, while the metathoracic leg is greatly spe- 

 cialized. The coxae of the former are not free and movable, 

 as in many insects, but immovably fixed to the thorax, and, 

 according to Witlaczil, coalescing with it. They are greatly 

 produced laterally, this portion being flattened and longer in 

 the mesocoxa than in the procoxa. 



The trochanters are short, cylindrical sclerites, somewhat 

 constricted proximally. All three pairs are similar. 



The two anterior pairs of femora are swollen, the outlines 

 of their dorsal surfaces somewhat convex, and the cuticula of 

 ventral surfaces much roughened. The femora of the protho- 

 racic legs are somewhat longer than those of the mesothoracic 

 pair. The distal ends are on their ventral faces deeply gouged 

 out, into which groove, bounded by strong lateral edges, the 

 tibiae fit when the leg is flexed. The femora of the metatho- 

 racic legs are similar in structure to those of the other pairs, 

 but longer and relatively more slender. There was very little 

 variation of this part, as may be seen by the following table of 

 measurements : 



AVERAGE LENGTH. 



Male. Female. 



Right. Left. Right. Left. 



0.656 mm. 0.654 mm. 0.686 mm. 0.691 mm. 



The articulation between femur and trochanter of meso- 

 thoracic leg is shown in figure 78, page 150. This is similar in 

 the other pairs. 



The structure of the tibiae is of great interest. The tibiae of 

 the prothoracic and mesothoracic legs are about as long as the 

 femora, but those of the metathoracic legs are slightly longer 

 than the femora. The distal ends of the first and second pairs 

 of tibiae bear a fringe of long, sharp spines which point distad, 

 those of the prothoracic pair being slightly the weaker. The 

 distal ends of the metatibiae are swollen and bear nine short, 

 thick, blunt, black spines (figs 73, 74 and 75). These spines 

 are a part of the scheme of specialization for jumping, pre- 

 venting the foot from slipping in the same way as do the 

 spines on the grasshopper's tibiae. 



The tarsi are two-segmented. In the first two pairs of legs 

 the second segment is larger, but the first is the larger in the 

 metathoracic pair. In all three pairs the segments are much 



