52 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 1 37 



they belong. In the arthropods, though the appendages constituting 

 the mouth parts of chewing forms are considered to be modified legs, 

 the actual working structures of the mandibles, maxillae, and the 

 labium where one is present, are formed from endite lobes of the two 

 basal segments of the telopodite according to Snodgrass (1935)- The 

 telopodite becomes reduced and acts as a sensory organ or, in the case 

 of the mandibles, is lost entirely. 



Though appendages of both the Onychophora and the Arthropoda 

 have had a common origin as lobiform outgrowths of the body wall, 

 nothing like the elaborate development of the leg of arthropods takes 

 place in the Onychophora. The differentiation of the onychophoran 

 leg into a thick basal part and a slender distal part, as Snodgrass says 

 (1938), might be seen as an incipient segmentation, but the develop- 

 ment of endite lobes on the basal leg segments of arthropods into the 

 chewing and crushing structures we call mandibles finds no parallel 

 development in the Onychophora. 



The "jaws" of Peripatus are simply the claws at the end of the 

 appendage, greatly enlarged when compared with the claws of the 

 walking legs but not greatly different from them in function. Tiegs 

 (1949) recognized this when he said that the "jaws" of Peripatus 

 were merely enlarged claws. Also they are not retracted simultane- 

 ously as are the mandibles of a chewing insect for example, but are 

 retracted alternately, according to Manton (1937). For these reasons 

 the term "jaws," though firmly established in the literature, is incor- 

 rect, and the organs should be designated as the "feeding claws." 



To understand how these claws work one must consider them as 

 the tip ends of greatly strengthened legs which have been withdrawn 

 into the body so that just the tips of the claws project into the oral 

 cavity (figs, i A, 2 A, B, C, D). The muscles then taking them from 

 the anterior to the posterior consist of the following groups : 



13. Anterior protractor of the claws (fig. i C, D, aprm), a powerful 

 group of muscles arising anteriorly on the head wall and inserted at 

 the base of the claws. (The apparent distortion of these muscles indi- 

 cated in the sketch is probably due to stresses put upon them by the 

 hooks holding the dissection in place.) 



14. The dorsal retractor of the claws (drm) consisting of widely 

 spaced fibers originating on the body wall above the slime gland ducts ; 

 inserted on the retractor apodeme of the claw. These muscles cor- 

 respond to branches, a, b, c, d, and e of the retractor of the claws as 

 described by Calora (1957). 



15. The ventral retractors of the claws (vrm) ; a broad fan of 



