ANATOMY AND PHYSIOLOGY 



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jOther tympanal organs, doubtless auditory, are found on the fore 

 tibiae of Tettigoniidae, 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, 

 consist each (Fig. 140) of a tense cord, probably capable of vibration, 

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



FIG. 139. 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; n, nerve; o, opening muscle 

 of spiracle; p, p, processes resting against tympan- 

 um; s, spiracle; tm, tensor muscle of tympanum; v, 

 vesicle. After GRABER. 



FIG. 140. Chordotonal sense 

 organ of aquatic dipterous larva, 

 Corethra plumicornis. cd, cord; eg, 

 chordotonal ganglion; /, fibers of an 

 integumental nerve; g, ganglion of 

 ventral chain; /, ligament; m, lon- 

 gitudinal muscles; n, chordotonal 

 nerve; r, rods (nerve terminations); 

 /, tactile setae. After GRABER. 



anterior end to a ligament. Between the cord and the supporting 

 ligament is a small ganglion, which receives a nerve from the principal 

 ganglion of the segment. 



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. 141) of (i) lens, (2) vitreous 

 body, (3) retina, (4) nerve fibers, (5) pigmented hypodermis cells, and (6) 



