86 



ENTOMOLOGY 



tibiae of Locustidae, ants, termites and Perlidae, on the femora of Pedicu- 

 lidae and the tarsi of some Coleoptera. 



Several types of chordotonal organs have been described, of which 

 those of the transparent Corethra larva may serve as an example. These 

 organs, situated on each side of abdominal segments 4-10, inclusive, con- 

 sist each (Fig. 138) of a tense cord, probably capable of vibration, which 

 is attached at its posterior end to the integument and at its anterior end 

 to a ligament. Between the cord and the supporting ligament is a small 



O M. 



#--'-, 



FIG. 137. Inner aspect of right tympanal sense 

 organ of a grasshopper, Caloptenus italicus. b, chitin- 

 ous border; c, closing muscle of spiracle; gn, gan- 

 glion; m, tympanum; w, nerve; o, opening muscle 

 of spiracle; p, p, processes resting against tympanum; 

 s, spiracle; tm, tensor muscle of tympanum; v, vesicle. 

 After GRABER. 



FIG. 138. Chordotonal sense 

 organ of aquatic dipterous larva, 

 Corethra plumicornis. cd, cord; eg, 

 chordotonal ganglion; /, fibers of an 

 inlegumental nerve; g, ganglion of 

 ventral chain; /, ligament; m, lon- 

 gitudinal muscles; w, chordotonal 

 nerve; r, rods (nerve terminations); 

 /, tactile setae. After GRABER. 



ganglion, which receives a nerve from the principal ganglion of the seg- 

 ment. 



Vision. The external characters of the two kinds of eyes ocelli and 

 compound eyes have already been described. While the lateral ocelli 

 are comparatively simple in structure, consisting of a small number of 

 cells, the dorsal ocelli almost rival the compound eyes in complexity. 



Dorsal Ocelli. These consist (Fig. 139) of (i) lens, (2) vitreous 



