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SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



The mandibles of Protura are not hollow. They are long spearlike 

 structures with a slitlike opening near the apex. Prell (1913, fig. 4) 

 describes a rod from the proximal apex to the wall of the head, but I 

 have not found this; perhaps it is the fanlike ligament (fig. 12) tak- 

 ing this aspect in certain views. Prell also describes the basal part of 



,p?-- 



0.05 mm 



Fig. iG.—Onychiurus armattis Tullb. Head, dorsal, with antennal and 

 mandibulary muscles (c-i) ; see text. 



the mandible of Eosentomon as hollow; the position of the muscles 

 in Acerentomon does not seem to support this observation. 



In figure 17 I have drawn the muscles of the mandibles as seen 

 by me; my figure agrees rather closely with the figure by Berlese 

 (1909, fig. 121). There are two sets of protractor muscles and two 

 sets of retractors, a median and a lateral one, all originating near the 

 proximal end of the mandible. The retractor muscles run to the 

 lateral and dorsal wall of the head, respectively ; of the protractors 



