STRUCTURE OF ONYCHOPHORAN HEAD — BUTT 5I 



12. The median extensors of the salivary pump. A group of small 

 muscles that are intimately associated with the small muscles under 6 

 (vld) . They appear to form an X underneath the common duct where 

 they attach to the body wall. Distally they insert along the edges of 

 the inner chamber, one anterior to the duct, the other posterior to the 

 duct on each side (fig. 3 C, mexp). 



The action of these muscles together with the lateral extensors ap- 

 parently straightens out the two chambers on each side, thus opening 

 up the passage between them ; in other words, they open the valve. 



Many other small fibers already assigned to muscle vld converge on 

 the center line at the same point. Others of this group lie on top of 

 the inner chambers and appear by their action to compress the inner 

 chambers. I did not find any other valve mechanism that would pre- 

 vent liquid from reentering the ducts when the compressor muscles 

 are relaxed. It may be that the action of the longitudinal muscles just 

 mentioned would accomplish this purpose by forcing the median cham- 

 bers closed when the lateral chambers are extended by the relaxation 

 of muscles 11 and 12. 



THE FEEDING CLAWS 



The "jaws" of Peripatus consist each of a pair of long, slender 

 claws (figs. I D, Fcl) protruding into the oral cavity from their bases 

 which are deeply invaginated within the body (figs, i A, 2 A, B). 

 Only their tips are to be seen lying across the mouth opening. 

 From their inner ends long apodemes (Apd) extend into the body 

 cavity, and to these, powerful muscles are attached. The muscles are 

 capable of acting as protractors or retractors, the retractor muscles 

 also acting as flexors of the claws. These organs have been the sub- 

 ject of a great deal of investigation, and many views have been pre- 

 sented as to their segmental relationships. Some German workers 

 apparently have been convinced not only that they are true jaws but 

 that they are homologous with the mandibles of the arthropods. How- 

 ever, though they lie almost in the same plane, they are not opposed 

 to each other and in fact do not in the least act as true jaws. They 

 are not crushers or chewers of food but they act instead as claws or 

 rakes with which the animal simply scratches particles of food away 

 from the food source so that other mechanisms of the ingestive ap- 

 paratus are able to move them into the mouth in a position to be 

 swallowed. 



Further comparison with the arthropod mandible reveals pertinent 

 facts which may give us a clue in identifying the segment to which 



