Xo. 641 diptera of Connecticut: morphology 63 



faces. The surfaces of the femur and tibia which are apposed when 

 the leg is folded together (like a knife) are called the ventral sur- 

 faces of these segments according to Grimshaw's terminology; but 

 these surfaces are frequently called the flexor surfaces by other dipter- 

 ists, who refer to the opposite surfaces as the extensor surfaces. 



Snodgrass (1927, p. 93) follows Boerner, Heymons, and other 

 German entomologists in considering that the pleural sclerites of an 

 insect represent the modified basal portions of the leg (called the sub- 

 coxa) of a crustaceoid arthropod, and compares the coxa with the cox- 

 opodite, the two parts of the trochanter with the basipodite and ischi- 

 opodite, the femur with the meropodite, the tibia with the carpopodite, 

 and the pretarsus with the dactylopodite, in interpreting the parts of 

 an insect's leg in terms of the parts of a typical crustacean limb. 

 Although such a comparison of the parts of the legs in the represen- 

 tatives of two distinct classes of arthropods is necessarily somewhat 

 speculative, it seems to be fairly well established that the pretarsus 

 (acropod), or region beyond the fifth tarsal segment, of an insect's 

 leg represents a distinct segment, the dactylopodite of a crustacean's 

 leg, as was first pointed out by de Meijere, 1901, although this small 

 region is usually overlooked by entomologists in describing the seg- 

 mentation of the leg of an insect. 



The coxa, ca?, articulates dorsally with the coxifer, c/, (Fig. 6, F) 

 or pleural process at the ventral end of the pleural suture. A sternal 

 articulation of the coxae of the meso- and metathorax is frequently 

 formed by two wing-like extensions (one on each side) of the fur- 

 casternum, which is folded between the middle coxae when they be- 

 come approximated mesally. 



The pro thoracic coxae are frequently more cylindrical than the 

 others, and in such empids as the one shown in Fig. 8, G, the pro- 

 thoracic coxae are extremely elongated and slender. The coxae of 

 most Mycetophilidae are quite elongated, although in most Diptera the 

 coxae are not as a rule greatly elongated even when the femur and 

 tibia become extremely elongated as is the case in the Tipulidae. In 

 such parasitic forms as the Hippoboscidae (Fig. 6, E and F), the 

 coxae are rather short and stout, and are quite mobile. 



The mesothoracic* coxae are divided into an anterior region or 

 eucoxa, ec^ and a posterior region or meron, ine^ in the tipulid shown 

 in Fig. 6, A; and the meron, me^ becomes increasingly closely asso- 

 ciated with the lower region of the epimeron, em, (Fig. 6, D), until in 

 the higher Diptera it unites completely with the lower portion of the 

 epimeron to form the composite region labelled nnyl in Fig. 6, C. In 

 such cases the eucoxa may become divided into a basal region, &ca?, 

 (which remains rather closely united with the region myl) and a 

 distal region, dcx^ which becomes detached from the rest of the 

 eucoxa, in order to restore the mobility of the basal region of the leg, 

 which is lost when the meron, etc., become united with the lower por- 

 tion of the epimeron. In such mycetophilids as the one shown in Fig. 

 <;. B, the meral region, me, unites with the lower portion of the epi- 



*The mesothoracic coxae of the mycetophiHd Mycomyia maxima bear long, slender, for- 

 ward-projecting- processes or "coxal spurs" which are developed only in the males. 



