V 



HEARING— FIELDWORK AND EXPERIMENTS 



Observations and experiments with the lower organisms 

 designed to inquire into their reaction to vibration have 

 already been mentioned and are comparatively easy to carry 

 out with the aid of even a low-power microscope. 



Larger Invertebrates 



With earthworms, their sensitivity to light is perhaps 

 exceeded by their reactions to vibrations. This can be 

 demonstrated by placing some worms on a piece of stiff 

 cardboard which has been moistened sufficiently to enable 

 the worms to move about freely. If a tuning-fork is struck and 

 then lightly brought into contact with the card, the worms 

 will retract in response. 



The same kind of experiment can be carried out with web- 

 spiders. A tuning-fork held very near, but not even touching, 

 the outer threads of the web will often bring the spider forth 

 from its lair, the vibrations causing the spider to react as if 

 an insect had touched the web. 



Caterpillars, too, will often behave in the same way if they 

 are feeding and the plant is touched gently. In fact, a very 

 wide variety of animals will show their response to vibrations, 

 though to us no audible noise is detected. 



Many insects use their peculiar hearing organs to receive 

 sounds made by their mates ; and this can be observed with- 

 out much trouble by capturing some grasshoppers or crickets 

 and confining a male in a container — even a paper bag 

 will do. If the month of the year and the time of day and 

 temperature are correct, the male insect will "stridulate" ; 

 and if some females are then liberated in the vicinity of the 



container, they will move towards it, thus showing not only 



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