98 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxvi. 



the structure of the pterothorax is evident in the wingless individuals 

 (Plate XI, fig. 125). The size of the pterothorax becomes greatly 

 reduced in such cases as no great muscular development is needed to 

 move the legs alone and the pterothorax is, perhaps, but little larger 

 than the prothorax. The dorsal plates of both segments lose the usual 

 form and become rectangular and transversly broadened, extending 

 over the membranous space which is usually present along each side. 

 No traces of wings are present and there is no longer any place for 

 them. As a consequence of the decrease in musculature the endo- 

 thoracic structures have become verv much weaker, though still plainly 

 visible. 



APPENDAGES OP THE THORAX: LEGS. 



The legs of Thrips are among their most characteristic structures 

 and can hardly be mistaken for those of any other insects, whether 

 short and powerfully thickened or long and slender. They are com- 

 posed of the usual parts of the insect leg, which may be readily dis- 

 tinguished. The attachments to the thorax are quite far apart and at 

 the very hind edge of each segment. The fore legs are often shorter 

 and thicker than the others and more specialized. 



Ooxa. — This basal segment is large, usually subconical and quite 

 freely movable. The fore coxte, especiall}^ in Phkeothripid;e, often 

 bear a few short, very stout, sharp spines and one long spine at tho 

 outside, but aside from these spines the coxae exhibit little that seems 

 to be worthy of note. 



T7'0Ghante?\— This is a short, small segment between the coxa and 

 the larger femur, its line of attachment with the latter being often 

 considerably oblique. 



Femur. — This, the first prominent segment of the leg, is quite long 

 and more or less cylindrical or fusiform. The fore pair is frequently 

 distinguished by much greater thickness than those of the other legs, 

 (especiall}^ in Phlceothripidse), the enlargement taking place in the upper 

 side of the base and diminishing toward the outer end. In ChlrotJtrq'S 

 the lateral surface is strongly chitinized and bent backward somewhat 

 at the tip so as to appear almost tooth-like at that point. In thickened 

 femora, especially, the inner side toward the base is grooved to receive 

 the base of the tibia when the latter is closed inward, and in a few 

 species with this kind of femur the angles here have become sharply 

 pointed and chitinized so as to form two sharp teeth at the tip (Plate 

 VIII, figs. 89, 90). 



Tihia. — The tibia is, as a rule, about as long as the femur and more 

 nearl}^ cylindrical or often club-shaped in form. It is most slender 

 near its base where it is often slightly bent. At the extremity within, 

 in a few species, the tibia bears an erect, stout, recurved hook or tooth 

 as it is usually called. 



