ORIGIN OF EAR. 



109 



clearly visible than in any which I had examined. 

 Fig. 70 represents part of the tibia of Isopteryx apicalis. 



These organs do not, however, appear to be univer- 

 sally present. In some very transparent species no 

 trace of them can be found. 



But though so similar in structure, and probably in 



Fig. 70.* — Part of the tibia of Isopteryx apicalis (after Graber). _ SOy Auditory organ ; 

 ef, terminal filament ; Cu, cuticle ; G, ganglion cells ; ef, terminal filaments ; tr, 

 trachea ; n, nerve. ' 



function, it may be doubted whether this tibial organ 

 in the ants can be traced to a common origin with that 

 of the Orthoptera. According to Graber, the direction 

 of the rods is reversed in the two cases, which he regards 

 as clear proofs that they have arisen independently. 

 He is even of opinion that the tympana themselves 

 have originated independently in the different groups 

 of Orthoptera. Moreover, Graber has found this organ 

 in certain insects not only in the anterior, but also ia 

 the two other pairs of legs. Indeed, rods of the same 

 character have been found in other regions of the body. 



* In this, as in one or two of the other figures, the explanation of 

 some of the lettering appears to be omitted in the original. At least, 

 I have been unable to find it. 



