NO. II LEGS OF PRIMITIVE ARTHROPODS — EWING I5 



should, therefore, be regarded as the tarsus. In the first and last legs 

 the last two segments only are without muscle origins. Apparently 

 segment six of the generalized legs has fused with seven to make the 

 single but very long sixth segment, in the first and last legs as claimed 

 by Kenyon (1895). 



Next to the three-segmented tarsus is the last segment giving rise 

 to muscle fibers. It is the longest segment and should be regarded as 

 the tibia. Proximal to the tibia is the stouter and shorter femur with 

 its adhering incomplete ring at the inner basal aspect. This rudiment 

 of a segment gives rise to no muscles. Such a condition, as well as 

 its fusion with the femur, indicates that it is the trochanter, yet con- 

 cerning this point there is not conclusive evidence. Dorsally the 

 femur gives rise to powerful flexor muscle fibers, some going to the 

 claws and some to the tarsus. Between the third segment and the 

 incomplete basal segment is a short but very broad segment which 

 bears ventrally a clavate appendage, regarded by some as being 

 analogous with the stylus of Thysanura. When this large segment is 

 compared with the coxa of a proturan leg it is observed that it not only 

 has a similar position in the leg series of segments but has the double 

 r(jcking type of hinge at both ends just as the proturan coxa has ; 

 however, the first segment is also decidedly like the coxa of many 

 generalized insects. Although the writer is inclined to recognize this 

 second segment as the first trochanter we are not sure that it is such. 

 Regarding the subfemoral segment as the true coxa leaves only the 

 decision that the incomplete basal segment is the subcoxa, yet if so 

 it is more completely developed than in any insect. In pauropods 

 this first segment is an integral part of the leg, although barely a 

 complete ring and with only a few levator muscle strands. The de- 

 pressors, however, are large and powerful (see pi. 4, fig. 8) . Although 

 the first segment is a mova1)le segment in P'auropoda, at the same 

 time it partakes of the nature of a body sclerite by sending upward 

 a long apodeme which* rests vertically in the body wall, rotating slightly 

 when the subcoxa is moved. 



THE SO-CALLED COXAL APPENDAGES IN PAUROPUS 



In Pauropus the two proximal segments of the legs bear on their 

 ventral surfaces conspicuous spatulate structures. In the posterior 

 legs these structures appear to be forked. A closer inspection, how- 

 ever, shows that those on the posterior legs bear laterally a clublike 

 appendage and are hardly biramous. These appendages have been 

 regarded by some as true vestiges of real segments and as homologous 

 with the coxal appendages of Symphyla and Thysanura. 



