yO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 89 



12. — Origin posterior to // on extreme posterior part of tenth 

 tergum; crosses internal to outer end of /i to insertion on dorsal 

 margin of base of cercus. This muscle Ford (1923) regards as a 

 muscle of the epiproct which has shifted forward to the tenth tergum, 

 since the corresponding muscle in some other Orthoptera arises on 

 the epiproct. 



/J. — Origin anterior on antecosta of tenth tergum above level of 

 cercus; goes posteriorly and downward to insertion on inner (pos- 

 terior) edge of base of cercus. 



il^. — Origin on antecosta of tenth tergum before lower end of cereal 

 base ; extends upward and posteriorly, ectad of ij, to insertion on 

 posterior dorsal angle of base of cercus. 



75. — A short muscle arising on antecosta of tenth tergum between 

 Jj and ih; insertion on anterior (outer) margin of base of cercus. 



16. — A short, fan-shaped muscle arising on ventral part of tenth 

 tergum ; fibers converging dorsally to insertion on ventral angle of 

 base of cercus. 



The number of muscles arising in the tenth segment inserted on the 

 bases of the cerci might seem to discredit the embryonic evidence that 

 the cerci are appendages of the eleventh segment. We can only sup- 

 pose that the muscles which function as motors of the cerci are 

 morphologically the dorsal intertergal muscles between the tenth and 

 eleventh segments that have secondarily become attached on the bases 

 of the cerci. The same assumption must be made for all other insects, 

 except with regard to the cereal muscles from the epiproct, but in 

 the Thysanura it is quite evident that the cereal muscles are the 

 normal longitudinal muscles of the tenth segment (fig. 22 D). 



Three muscles take their origin in the tenth segment of Grylliis 

 that are not attached on the cerci. 



7p7. — A short intersegmental muscle arising on ventral end of tenth 

 tergum (fig. 22 C) ; inserted posteriorly on anterior margin of para- 

 proct. 



iS. — Dorsolateral muscle of the rectum, arising dorsally on tenth 

 tergum above ij. 



/p. — Ventrolateral muscle of the rectum, arising ventrally on tenth 

 tergum in angle between 16 and //. 



The following muscles are confined to the eleventh segment : 



20. — A pair of slender, median, dorsal muscles, arising on anterior 

 end of epiproct (fig. 22 C) ; inserted posteriorly on extremity of 

 dorsal wall of rectum. (The supra-anal muscles of Ford.) 



