762 General and Applied Biology 



its buzzing sound by completing 330 wing strokes per second. Many 

 insects, especially those with heavy, chitinous exoskeletons, possess spines 

 and hairs attached to nerves by means of which they recognize or "feel" 

 sound vibrations. 



In lower fishes the ear is primarily affected by stimuli produced by 

 changes in the position of the fish. Hence, such fishes maintain a typical 

 position with respect to their surroundings. Well-developed vocal cords 

 and organs of hearing appear only in terrestrial vertebrates. Eardrums 

 and vocal cords are not present in fishes. Amphibia (frogs, toads) have 

 the simplest of vocal cords. It seems that the developments of sound- 

 production and sound-reception mechanisms go together and that they 

 are rather closely correlated. Male and female frogs (Rana pipiens) 

 produce different kinds of croaking sounds by forcing air back and forth 

 from the mouth cavity and lungs across their vocal cords. Frogs produce 

 a "pain scream" when caught, a "grunting" sound when satisfied, an 

 "alarm cry" to tell others to seek safety. In the ears of higher vertebrates 

 (Fig. 250) the semicircular canals function as an organ of equilibrium, 

 while the cochlea ("snail shell") receives sound waves and sends them 

 over the auditory nerve to the brain. The human vocal apparatus and 

 ears are described elsewhere. 



Bioluminescence and Light 



Bioluminescence may be defined as the phenomenon of light produc- 

 tion by living organisms apart from incandescence (light with heat). 

 Light may be defined as the form of radiant energy, the waves of which 

 act on the eye so as to render visible the object from which the light 

 comes. Light waves travel approximately 186,000 miles per second. 

 Bioluminescent light is known as cold light because only 1 per cent is 

 invisible heat rays. This is the most efficient light known. Luminous 

 cells of plants and animals secrete granules containing luciferin, which 

 glows in the presence of oxygen when activated by the enzyme lucijerase. 

 Luminescence is displayed by such animals as the firefly (beetle), the 

 glowworm, certain squids and fishes, certain jellyfishes and shrimp, cer- 

 tain species of Protozoa, etc. In the firefly, photogenic organs containing 

 localized masses of fatty substances produce a very efficient light by 

 oxidizing the fatty substances. The photogenic organs are well supplied 

 with oxygen by a copious supply of tracheal tubes. The greenish-yellow 

 light has few nonluminous rays. Its emission appears to be controlled by 

 the nervous system by regulating the oxygen supply. These photogenic 

 organs are associated with sexual attraction, the female generally produc- 



