EXERCISE 94 \ t .-/, \ 



Vibrations of certain kinds are received through the ear and interpreted as sound. In different 

 kinds of animals these vibrations are perceived through other kinds of organs, as by hairs on the 

 antennae of mosquitoes and the "drums" on the front legs of crickets. 



Problem. What kinds of ears have animals other than mammals ? 



What to use. Living or preserved frog and grasshopper ; magnifier. 



What to do. Study the external eardrum of the frog and the tympanum of the grasshopper on its 

 first abdominal segment, for size, shape, and rigidity or flexibility. If you have live specimens, determine 

 whether they are sensitive to sounds that are different in pitch, loudness, or other quality. 



Record. Describe results of your observations. Make diagrams showing structures. 



Questions. 1. What organisms do you know that are not affected by sounds ? 



2. How do you know they are not affected ? 



3. Under what living conditions would perception of sounds be of no use to an organism ? 



4. What practical applications are made of the principle of vibration illustrated by the action of an 



eardrum ? 



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