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SMITHSONIAiSr MISCELLANEOUS COLLECTIONS VOL. 85 



wall often marked by distinctive groups of setae (fig. 3 A) ; distally 

 the leg ends in a retractile lobe (Vs), called the planta, which bears 

 the claws, or crochets (d). 



Functionally the planta is the most important part of the leg, and 

 structurally it is the most variable. The proximal parts of the ap- 

 pendage dififer principally in relative size in different species. The 

 planta in its more generalized condition is a short cylindrical pad with 

 a circular distal surface, on the center of which is inserted a group 



Fig. 37. — Structure of an abdominal leg of a caterpillar. Malacosoiiia 

 ainericana. 



A, posterior view of a pair of abdominal legs. B, ventral view of a left ab- 

 dominal leg, showing crochets {d) turned outward, and insertion of retractor 

 muscles (c) at inner margin of plantar lobe (I's). C, dorsal view of leg mus- 

 culature, right side. D, posterior view of musculature of a right leg. 



a, dorso-pleural groove ; Cx, coxa ; d, crochets ; e, insertion point of retractor 

 muscles of planta; mb, membranous area between subcoxa and coxa; rvs, 

 retractor muscles of planta; Sex, subcoxa; Vs, planta (retractile vesicle). 



of retractor muscle fibers. In such cases the crochets may be arranged 

 in a complete circle around the distal plantar surface, with their re- 

 curved points turned peripherally and upward. With most cater- 

 pillars, however, the claws are limited to a semicircle or a small arc 

 usually on the inner margin of the planta (fig. 37 B), and in such cases 

 the planta itself {Vs) generally becomes asymmetrical by a reduction 

 or obliteration of its outer half. The planta then assumes the form 

 of a lobe projecting to the mesal side of the axis of the limb, marked 

 by the insertion point of the retractor muscle {c), and its claws {d) 



