34 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I42 



Hphy 



Fig. 16. — Evolution of the tentorium. 



A, Scutigera sp., Chilopoda, ventral surface of anterior part of head with 

 mouth parts removed, showing hypopharyngeal fulturae {hF) and their apodemes 

 (Ap). B, Lithobiiis sp., Chilopoda, same view of head as A. C, Scutigerella 

 immaculata, Symphyla, optical section of head behind mandibles. D, Neso- 

 inachilis maoricus, Thysanura, posterior view of interior of head, showing sepa- 

 rate anterior tentorial arms {AT) and tentorial bridge (TB). E, Isonycftia sp., 

 Ephemeroptera, larval head, posterior, showing tentorium. F, Anax Junius, 

 Odonata, larval tentorium, dorsal. G, Strophoptcryx jasciatus, Odonata, larval 

 head, anterior. 



central plate, which rests against the posterior bridge, or overlaps it, 

 but does not unite with it. In both thysanuran families slender 

 dorsal arms (D, DT) branch from the anterior arms and are at- 

 tached on the cranial wall by small groups of muscle fibers. 



