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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



senting the phylogenetic origin of the definitive pleural plates and the 

 leg bases. It would seem more probable that they are ontogenetic phe- 

 nomena only, and that Becker's observations really show simply that 

 the pleurites and the bases of the legs have a common origin. 



In the decapod crustaceans the inner walls of the gill chambers, 

 which are covered externally by lateral folds of the carapace, are 

 formed of large cuticular plates bearing the gills (fig. 7 D). Each 

 plate, or pleuron, shows subdivisions (ScXiScxa) corresponding with 

 the body segments of the ambulatory legs, and each subdivision bears 

 a gill {Brni-Brns) . In the second maxilliped (B) the homologue of 

 the gill is borne on an epipodite (Eppd) which is distinctly carried by 



Sex 



A Cx Stn 



Fig. 8. — A body segment of Strigamia bothriopiis (Chllopoda, Geophilidae). 



A, lateral view, with leg removed beyond the coxa. B, ventral view, including 

 bases of legs. Cx, coxa ; 1st, intersternite ; pi, pleurites between the tergum and 

 the subcoxa ; Sex, subcoxa ; Sp, spiracle ; Stn, primary sternite ; T, tergum ; Tr, 

 trochanter. 



the basal segment of the appendage, or coxopodite {Cxpd). In the 

 third maxilliped (C), however, the gill arises from a subcoxal part of 

 the limb basis {Sex). In the ambulatory region (D) the gills on the 

 pleuron are successively more and more removed from the coxae. It 

 thus becomes evident that the pleural wall of the branchial chamber in 

 the decapod crustaceans has been formed from dorsal extensions of 

 the subcoxal parts of the leg bases, and that the coxae have acquired 

 special articulations with the subcoxae. In the majority of crustaceans 

 the leg base is an undivided coxopodite. 



In the Chilopoda there is a definitely circumscribed subcoxal area 

 about the base of each leg, which may be continuously sclerotized, as 

 in Strigamia (fig. 8 A, Sex), or which may contain one or more 

 sclerites, as in Lithobius (fig. 9), Seolopendra, or Scutigera (fig. 10). 

 The coxa is usually articulated to a sclerotized part of the subcoxa 

 dorsally (fig. 10 A, c) , or ventrally (figs. 9, 15, d) ; but since the axis 



