STRUCTURE OF ONYCIiOrilORAN HEAD BUTT 59 



ing claws have withdrawn into this cavity. Also a cephalic movement, 

 accompanied by a dorsal movement, of the ventral organs around the 

 stomodaeum has commenced. This leads to alterations in position and 

 even to distortion of the ventral organs involved. I, therefore, feel 

 that placing full reliance upon such sections is not justified. 



Pflugfelder's efforts to prove the presence of a premandibular seg- 

 ment would be more acceptable if he had found such a segment at an 

 earlier stage before the preoral cavity had begun to form. 



Both Pflugfelder and Federov apparently base their theory of head 

 segmentation in the Onychophora on the assumption that the feeding 

 claws are true mandibles, and the necessity to interpolate another seg- 

 ment between the antennal and the mandibular segments has led them 

 into complicated reasoning that is hard to follow. The earliest stages 

 in which segmentation appears have always been accepted as the stages 

 that determine segmentation in any form, and the Onychophora should 

 not be considered as exceptions to this rule. 



SUMMARY 



The head of Peripatiis is an undifferentiated region without grooves 

 to mark its segmental areas. The head appendages are the antennae, 

 the feeding claws, and the slime papillae. There is no labrum, the pre- 

 oral cavity being surrounded by oral lobes constituting the lips, the 

 dorsal lobe of this group forming a structure similar to the epipharynx 

 of insects. The dorsal lobe aids in the ingestion of food. The feeding 

 claws are not homologous with mandibles but rather correspond to the 

 transitory labral lobes found in some insect embryos. This is indi- 

 cated by the following facts : 



1. They are innervated by the third or tritocerebral segment of the 

 brain. 



2. They do not function as mandibles or chewing jaws but more as 

 scratching claws. 



3. The coelomic sacs of the feeding claw segment are located im- 

 mediately behind the antennal coelomic sacs. 



4. The ventral organs of the feeding claw segment form the third 

 or tritocerebral lobes of the brain. 



5. The feeding claws do not form from ental lobes of the basal leg 

 segments as in insects, but are simply greatly strengthened claws de- 

 veloped from a much altered walking leg. 



REFERENCES 



Calora, F. B. 



The gross anatomy of Pcripatoidcs novac-zcalandiae (Hutton). Un- 

 published thesis, 1957, Cornell Univ., 41 pp., 18 figs. 



