Sounds emitted by Flies 97 



it is set iu action by sound-waves, which throw the setae 

 into vibration ; these vibrations he believed to be trans- 

 mitted through the antenna to the cup or enlarged joint, 

 and to the corpusculate fluid which he supposed to fill it. 

 and which he compares to the endolymph of the verte- 

 brate ear. The vibrations are ultimately communicated to 

 the fibres of the antennary nerve. These early investiga- 

 tions are commemorated by the name oi Johnston' s organ, 

 often given to the structures contained in the enlarged 

 second joint of an insect's antenna. 



The American phy.sicist, A. M. Mayer (1874), made 

 some interesting experiments on live gnats, glued to 

 slips of glass. Tuning-forks were sounded in the neigh- 

 bourhood of the gnats, and Mayer observed that some 

 of the setae of the antennae were thrown into vigorous 

 movement, especially when the fork Ut 4, giving 512 

 vibrations per second, was sounded. The forks Ut 3 

 and Ut 5 also set up more vibrations than intermediate 

 notes. Other setae responded to other notes. We have 

 repeated Mayer's experiments with the same general 

 result. The fork Ut 4 caused a great amount of vibra- 

 tion in the setae of Culex nemorosus^ affecting not 

 merely a few setae of particular length, but many 

 setae together; other forks produced a much smaller 

 effect. 



Mayer points out that the auditory hairs whose direc- 

 tion is transverse to the path of the sound-waves are 

 most powerfully acted upon, while those which point to 

 or from the source of sound are least affected. Hence 

 the male can judge of the direction in which the female 

 is to be found. 



We have next to inquire what sounds the female Sounds 

 emits which the male fly can perceive. On this point by flies. 

 the observations and experiments of Landois (1867). 

 though not made upon Chironomus, are instructive. 



MIALI.. JI 



