392 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I37 



tions that the proximal part of the labium is dissolved after having 

 been overgrown by the plicae, vt'hich leave between them the ventral 

 groove. A thorough study of the labium and its musculature in Col- 

 lembola in the same fine way as the study by Bitsch on Diplura is 

 much needed. 



Fig. 8.—0nychiurns armatiis Tullb. Head with mandibles, dorsal, {x and y, 



see text.) 



Figures 12-14 show the mouth parts of Acerentomon doderoi Silv. 

 as an example of the conditions in Protura. Berlese (1909) has 

 given excellent descriptions and in his figures 128-135 (Tav. XIII) 

 most enlightening cross sections of the head. In 1952 I myself pub- 

 lished other drawings dealing especially with the so-called tentorium, 

 the fulcrum. 



The main points are the following : The maxillae are hollow on the 

 inner side, whereas the mandibles are not hollow. A fulcrum, the 



