36 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I42 



teroid and other lower insects with strong biting and chewing man- 

 dibles, the tentorium may be strengthened by the development of 

 a central plate, the "corpotentorium," in which the four arms are 

 united (C, CT). In the higher insects the tentorium retains more 

 of the primitive form (A), but the relative thickness of the arms 

 is variable. The anterior arms may form a pair of strong longitudi- 



(J) pt Gu. 



Fig. 18.— Head and tentorium of a soldier termite, Termopsis sp. 



A, Undersurface of head, posterior tentorial pits (/>0 greatly elongate. 

 B, Cross section of head, posterior, showing tentorium in place. C, The ten- 

 torium, dorsal, tentorial bridge {TB) elongate. 



nal bars through the head, connected by a narrow bridge (D), or 

 the bridge may be strongly developed and the anterior arms reduced 

 to mere threads (E). The bridge is nearly always retained in some 

 form, but the component arms may be reduced to mere stubs giving 

 attachment to very attenuated anterior arms (F). An unusual modi- 

 fication of the tentorium is seen in the soldier caste of a termite 

 (fig. 18 B, C). The bridge {TB) is here drawn out longitudinally 

 into a long, inverted trough, from the anterior end of which diverge 

 the short anterior arms {AT). On the undersurface of the head (A) 

 it is seen that the "pits" {pt) are long grooves at the sides of the gula. 



