io8 



ENTOMOLOGY 



FIG. 138. 



faces of the membrane is equalized by means of an adjacent 

 spiracle, which admits air to the inner surface. Resting 

 against the inner face of the tympanum are two processes 

 (Fig. 137, p, p), which serve probably to transfer the vibra- 

 tions, and there is also a delicate vesicle connected by means 



of an intervening ganglion 

 with the auditory nerve, which 

 in this case comes from the 

 metathoracic ganglion. The 

 nerve terminations consist of 

 delicate bristle-like processes 

 which are probably affected by 

 the oscillations of the fluid con- 

 tained in the vesicle just re- 

 ferred to. 



Other tympanal organs, 

 doubtless auditory, are found 

 on the fore tibiae of Locustidje, 

 ants, termites and Perlidse, on 

 the femora of Pediculidse 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, situ- 

 ated on each side of abdominal 

 segments 4-10, inclusive, con- 

 sist each (Fig. 138) of a tense 

 cord, probably capable of vibra- 

 tion, 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 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. 



Chordotonal sense organ of aquatic 

 dipterous larva, Corethra plumicornis. 

 cd, cord; eg, chordotonal ganglion; f, 

 fibers of an integumental nerve; g, 

 ganglion of ventral chain; /, ligament; 

 m, longitudinal muscles; n, chordotonal 

 nerve; r, rods (nerve terminations); t, 

 tactile setae. After GRABER. 



