NO. I INSECT THORAX — SNODGRASS 33 



bears the basal attachments of the abductor and adductor muscles of 

 the coxa (Cx). In short, either the facts are most deceptive, or the 

 ticks have retained subcoxas in the form of functional leg bases. 



A recent writer, P.ecker (1923, 1924), would, in a manner, reverse 

 the relations between the pleuron and the base of the leg, since he 

 claims that in the Chiloi)oda and the Insecta the coxa and trochanter 

 are derived from the pleuron, the latter being a primary part of the 

 thoracic wall. Becker's claim, however, may be simply another way 

 of stating that the pleuron and the base of the leg are parts of the 

 same structure. 



Though it must be admitted that direct evidence for the derivation 

 of the insect pleuron from the base of the limb is still insufficient, 



zTr 



Sex 



Sex 



Fig. 17. — Legs of Acarina. 



A, hind leg of Amhlyomma tuberculatJim, ventral view; B, base of hind leg of 

 Dcrmaccntor t'orinlafiis. Cx, coxa; F, femur; Ptar, pretarsus ; Sex, subcoxa, 

 or ventral plate of body wall bearing free part of limb; Tar, tarsus; Tb, tibia; 

 iTr, first trochanter; 2Tr, second trochanter. 



there are many facts that may be adduced as circumstantial evidence. 

 In a cicada nymph, for example, each leg is attached to a large, oval, 

 subcoxal, latero-ventral area of the body wall between the tergum 

 and the sternum of its segment (fig. 7, A, Sex). The lateral part of 

 each area is occupied by the pleural sclerites (figs. 7 A, 15 B, 16 D), 

 and the precoxal and postcoxal parts (fig. 15 B, Acx, Pcx) are con- 

 tinuous in a semi-membranous fold around the mesal side of the base 

 of the coxa (fig. 7 A). Even in the adult, the mesal subcoxal fold 

 is quite distinct from the true sternum (fig. 7 B), though it is here 

 chitinized and appears as an elevated marginal rim of the sternum. 

 This structure recalls Heymons' statement that the adult sternum in 

 the Hemiptera includes the ventral part of the subcoxa. The pleurites 

 of a young cricket (fig. 26 A) and of other Orthoptera in the first 

 instar likewise give the impression of belonging to a basal leg seg- 



