102 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 8o 



13. The legs of insects have undergone an evolution that has re- 

 sulted in the typical leg structure of the adult, but various develop- 

 mental stages are preserved (in the legs of some of the lower insects, 

 and in those of certain larval forms. The third and fourth segments 

 of the primitive limb, the basipodite and the ischiopodite, have united 

 into a single small segment, the trochanter. The trochantero- femoral 

 joint, when movable, preserves its vertical axis of motion, with dorsal 

 and ventral articulations. A reductor femoris muscle persists, but 

 there is no productor. The femoro-tibial and tibio-tarsal joints have 

 lost their primitive monocondylic structure in most adult insects, 

 and have become dicondylic through the development of anterior and 

 posterior articulations, with the acquisition of levator muscles. The 

 tarsus, or propodite of the primitive limb, has become fragmented into 

 a series of sub-segments, typically five, but none of these sub-segments 

 have acquired muscles. The terminal leg segment, the dactylopodite, 

 has developed into the complicated pretarsus of most adult insects 

 through the suppression of the original median claw, and the develop- 

 ment of lateral claws, a median arolium, or various other accessory 

 lobes. A levator muscle of the dactylopodite is lacking in all insects ; 

 the depressor, with branches arising in the tibia, femur, and even 

 the trochanter, is retained as the " retractor " of the claws, the fibers 

 of its branches being inserted on the retractor apodeme, or " tendon," 

 attached to the unguitractor plate in the base of the pretarsus, possibly 

 a remnant of the original dactylopodite. 



ABBREVIATIONS USED ON THE FIGURES 



A, anal veins. B, oblique dorsal muscle. 



longitudinal dorsal muscle, indirect Ba, basalare, episternal epipleurite 

 depressor of wing. (parapteron). 



Ah, abdomen. Bs, basisternum. 

 Ac, antecosta. 



ac, antecosta! suture. C, costa, first vein of wing. 

 Acx, precoxal bridge. tergo-sternal muscle, indirect ele- 



A\Tn A. • 4. 1 • vator of wing. 



ANP, anterior notal wing process. ^, , 



. Cla, claw. 



Ant, antenna. ^. .-. r-t^u ■ c • 



Cn, cubitus, tilth vein 01 wing. 

 A/^h, anterior phragma. ^^^ ^^^^j^.^ ^^^^^ 



Apl, anapleurite. (^^ coxa. 



Ar, arolium. CxC, coxal cavity. 



Axv, prealar process, or bridge. c.xP, pleural coxal process {b). 



Ax, axillaries. lAx, first axillary ; 



2 Ax, second axillary ; sAx, D, muscle of third axillary, flexor of 



third axillary ; lAx, fourth wing. 



axillary. Dae, dactylopodite. 



