464 Dynamic Theory. 



crick is inaudible, the gnat that cannot hear the singing wings of his 

 brother. Insects are not exempt from the vicissitudes to which the 

 rest of animated nature is exposed, and there is the same necessity in 

 their -case, as much as the rest, to know the running water by its mur- 

 mur, the moving wind by its sighing or its roaring, the storm by its 

 thunder and the patter of the rain. That insects may possess organs 

 more easily impressed than ours is not improbable. They may hear 

 sounds so faint and soft as to be quite unable to agitate our heavier ap- 

 paratus, but their pitch must include ours substantially. 



The hum of a bee produced by the vibration of the wings, while gath- 

 ering honey is pitched on A ' , the rate of which is 440 per second. When 

 tired, however, he comes down to E ' , 330 per second, but when excited 

 or angry the pitch becomes different. 



Beside the sound made by its wings, the fly has a voice produced by 

 the stigmata of the thorax. This sound can be heard when the wings 

 and other parts of the body are held still, or even cut away. ( Packard 

 Study of Insects.) Many insects seem to be endowed with hearing 

 organs in more than one part of the body. In a great many there are 

 such organs in the antennae. In the grasshopper tribes and in ants and 

 some other insects the hearing organs are in the front legs. These hear- 

 ing organs include a series of vesicles each connected with a nerve fibril, 

 and each containing an auditory rod. These auditory rods are peculiar 

 to insects. 



FIG. 204. Ear of Rhopalonema, a Jelly-fish. 

 (Compare with ear of Ontorchis fig. 203.) 



FIG. 203. Ear of Ontorchis, a 



Medusa or Jelly-fish, 

 c. Cells, 

 o. Otoliths (ear-stones). 



The body of the organ is an 

 open pit situated on the margin 

 of the umbrella. The cells and 

 otoliths are connected by nerve 

 fibres which are continued in- 

 ward to the inner nerve ring. 

 The number of these organs is 

 60 to 80; but in some species 

 there are as many as 600. 



( Geyenbauer.) 



This ear is developed from a Tentacle. 



Me Modified Tentacle. 



o. Auditory Organ. 



s. Cup-shaped space nearly enclosed. 



( After Hertwig.) 



The auditory organs of the jelly-fishes are ranged around the margin 

 of the umbrella, and are very numerous, in some genera running as high 

 as 600, but in others from 60 to 80. The organ is more complicated in 

 some than in others. In some it is a mere open pit or vesicle lined with 

 cells, some of which contain otoliths, while others support auditory 



