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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 82 



The theory of the origin of the principal pleural sclerites of the 

 Chilopoda and Hexapoda from subcoxal segments of the legs has 

 much in its favor. There is little evidence, however, that a subcoxa 

 is a primary segment in the general arthropod appendage. The limb 

 bases of the Arachnida, Xiphosura, and most Crustacea are the primi- 

 tive coxae (coxopodites), for there can be no doubt of the identity 

 of the coxo-trochanteral articulation in all arthropods. The writer 



WP 



^/vp 



Mer 



Fig. 14. — The mesopleuron and base of the middle leg of a scorpion fly, 

 Panorpa consiietudinis. 



A, external view. B, internal view, showing muscles, a, accessory sclerite 

 of basalar lobe ; Ba, basalar lobe of episternum ; bcs, basicostal suture of coxa ; 

 Bex, basicoxite; Cx, coxa; Epm, epimeron; Eps, episternum; M', basalar 

 muscle ; M", subalar muscle ; Mer, meron ; O, levator muscle of trochanter ; 

 PIS, pleural suture ; Sa, subalar sclerite ; WP, pleural wing process. 



clearly was mistaken in suggesting in a former paper (1927, p. 33) 

 that the large basal leg segments of the ticks (Ixodoidea) are sub- 

 coxal ; and he now believes that the segmentation of the arachnid limb 

 can be given an interpretation different from that proposed by Ewing 

 (1928), who would make the basal segment in most cases a subcoxa. 

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

 already been pointed out, are evidently expansions of the subcoxal 

 regions of the bases of the ambulatory legs, to which the coxae of the 

 latter have become articulated ; but there is no evidence of the pres- 

 ence of subcoxal segments in the limbs of the more generalized Crus- 

 tacea. In the myriapods and insects, moreover, as the writer has else- 



