no 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL, 85 



odite in the phalangid or crustacean leg (A, B, C, f-g) is that be- 

 tween the coxa and the trochanter (D, f-g). The coxa {Cx), how- 

 ever, is separated from the tergum (T), and often from the sternum 

 (Stn), by a sclerotization, known as the " pleuron " (Sex), occupying 

 the position in the lateral wall of the supporting body segment that is 

 occupied by the limb basis in the phalangid and crustacean (A, B, C, 

 LB). In other words, the basal region of the appendage in the case 

 of the insect leg (D, LB) is composed of two parts (Sex, Cx) cor- 



iTr 



Fig. 46. — Basal parts of arthropod legs. 



A, third right leg of a phalangid, Liobununi, showing limb basis (coxopodite) 

 elongate ventrally (LB), turning antero-posteriorly on dorsoventral axis (a-b), 

 with telopodite movable dorsoventrally on horizontal axis (f-g). 



B, last right arnbulatory leg of a crustacean, Anaspides tasmaniae, with small 

 basis, or coxopodite (LB), on which the telopodite turns dorsoventrally on hori- 

 zontal axis (f-g) of first trochanter, or basipodite (iTr). 



C, leg of an isopod crustacean, Porccllio, with elongate basis, or coxopodite 

 (LB), to which the telopodite is articulated by a horizontal hinge (f-g) as in 

 A and B. 



D, mesothorax and middle leg of a young acridid nymph, Melanoplus, showing 

 region of limb basis (LB), between the horizontal baso-telopodite hinge (f-g) 

 and the tergum (T), subdivided into subcoxa (Sex) and coxa (Cx). 



_ a, dorsal articulation of limb basis with body; a-b, axis of articulation of 

 limb basis with body ; c, dorsal subcoxo-coxal articulation ; Cx, coxa ; Cxpd, 

 coxopodite (limb basis) ; f-g, axis of baso-telopodite hinge; Fm, femur (merop- 

 odite) ; h-i, axis of hinge between first and second trochanters; j-k, axis of 

 trochantero-femoral hinge; LB, limb basis (coxopodite); Sex, subcoxa; Stn, 

 sternum; T, tergum; iTr, first trochanter (basipodite) ; 2Tr, second trochanter 

 (ischiopodite). 



responding with the single plate or segment (coxopodite) forming the 

 basis of the arachnid and crustacean appendages illustrated (A, B, C). 

 A condition similar to that in the insect thorax is found, however, 

 in the thoracic region of the decapod crustaceans, where a large 

 pleural plate occurs on each side of the body intervening between 

 the coxae and the tergum. This plate is clearly a composite structure, 

 the segmental areas of which are evidently derived from the sub- 

 coxal parts of the leg bases, because they support the gills of the 



