288 



TEXT-LOOK OF h:.\T<)M< >U >< i V 



function, and about which there can be no reasonable doubt, and 

 then consider the more problematical organs, closing with an account 

 of the extremely various means of producing sounds and cries. 



The ears or tympanal and chordotonal sense-organs of Orthoptera and 

 other insects. The ears or tympana of locusts (Acrydiidse) are situ- 

 ated one on each side, on the basal joint of the abdomen, just behind 

 the first abdominal spiracle. That this is a true ear was first sug- 

 gested by J. Miiller, and his opinion was confirmed by Siebold, Ley- 

 dig, Hensen, Graber, Schmidt, Lubbock, etc. 1 



FIG. 290. Ear of a locust (Citloptenus itaiicus), seen from the inner side: T, tympanum; 

 TR, its border; o. u, two horn-like processes: bi. pear-shaped vesicle; n, auditory nerve; go, 

 terminal ganglion ; st, stigma ; m, opening, and m', closing, muscle of the same ; Jf, tensor muscle 

 of the tympanum membrane. After Graber. 



The apparatus consists of a tense membrane, the tympanum, sur- 

 rounded by a horny ring (Fig. 290). "On the internal surface of 

 this membrane are two horn-like processes (o, 11), to which is attached 

 an extremely delicate vesicle (bi) filled with a transparent fluid, and 

 representing a membranous labyrinth. This vesicle is in connection 

 with an auditory nerve (n~) which arises from the third thoracic 



1 Forel, however (Recueil Zoologique Siiisse, 1887), denies that these tympanic 

 organs are necessarily ears, and thinks that all insects are deaf, with no special 

 organs of hearing, but that sounds are heard by their tactile organs, just as deaf- 

 mutes perceive at a distance the rumbling of a carriage. But he appears to overlook 

 the fact that many Crustacea, and all shrimps and crabs, as well as many molluscs, 

 have organs of hearing. The German anatomist Will believes that insects hear only 

 the stridulation of their own species. Lubbock thinks that bees and ants are uot 

 deaf, but hear sounds so shrill as to be beyond our hearing. 



