66 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 85 



coxa supports the six-segmented telopodite (fig. 26, Tlpd), the proxi- 

 mal segment of which, or first trochanter (iTr), is articulated to the 

 coxa by a typical coxo-trochanteral hinge (fig. 25 B, f-g). Surround- 

 ing or partly surrounding the base of the coxa, in most of the pre- 

 genital segments but the last, is an area of the body wall containing 

 one or several small sclerites (fig. 27 A, Sex). These sclerites appear 

 to belong to the subcoxal region of the primitive limb basis, since 

 upon this region are inserted the tergal muscles of the appendage, and 

 within it arise muscles of the coxa. The coxa turns antero-posteriorly 

 upon the subcoxa by an approximately dorso-ventral axis (fig. 25 B, 

 c-d). 



The large terminal pair of legs of a chilopod borne by the last pre- 

 genital segment (fig. 27 A, Tlpd) are supported each upon a single 

 large plate in the lateral segmental wall (LB). The basal joint of each 

 of these legs clearly corresponds w^ith the coxo-trochanteral joints of 

 the preceding appendages, and a comparison of the leg-bearing plate 

 of this segment (LB) with the coxal and subcoxal sclerites of the 

 segments immediately anterior to it leaves little doubt that the single 

 " pleural " plate of the last segment represents both the coxa and the 

 subcoxa of the preceding segments (Cx, Sex). In other words, the 

 large pleural plates supporting the legs of the last pregenital segment 

 are the limb bases (LB) undivided into coxal and subcoxal parts as in 

 the other segments. The condition here, of course, may l)e the result 

 of a secondary union of the subcoxal sclerotizations with the coxa, 

 but it gives a convincing demonstration of the potential unity of the 

 coxal and subcoxal regions of the limb basis, and at least suggests 

 a primitive condition in which the limb basis occupied the lateral walls 

 of the body segment between the tergal and sternal plates (A, C, IT, 

 IStn) . The levator and depressor muscles of the telopodite of the 

 last pair of legs arise on the plate of the limb base and on the 

 sternum (D, O, Q) , and have their insertions on the first trochanter 

 (fTr). " ■ 



The basal structure of the last pair of legs in the chilopoda is 

 paralleled exactly in that of the legs of more generalized Arachnida 

 as in the Phalangidae (fig. 46 A), in which the free part of each leg 

 is supported on a large basal plate (L5) implanted in the lateral wall 

 of the body. Borner (1904) regards the single basal plate of the 

 terminal pair of chilopod legs as the united coxa and subcoxa ; but in 

 the Arachnida, he concludes (1921) that sulicoxae are absent and that 

 the plates supporting the telopodites are the coxae alone. It is not 

 clear why structures so evidently similar should be differently inter- 

 preted. 



