Biochemical and Biophysical Phenomena 761 



All energy eventually tends to be resolved into heat which cannot be 

 resolved in turn into other energies. Consequently, the energy of the 

 sun is constantly required to replace that which has become a useless 

 waste. Animals to a limited extent, and green plants to a great extent, 

 depend on the sun for this supply of heat. From these green plants 

 this heat is transferred to animals. Kinetic energy usually produces 

 heat. For example, a moving body encounters more or less friction and 

 consequently causes a certain amount of heat to be produced. Potential 

 energy may possess large quantities of latent heat which must be liber- 

 ated in some manner or other before they are available. 



Production and Reception of Sound 



The vibration of some sounding body produces sound waves which 

 are borne to, and interpreted by, a specialized organ, such as the ear of 

 higher animals. The plants and lower animals do not produce sounds 

 in the accepted sense, although they may be affected by sound waves in 

 certain instances. In several higher animals sounds are produced and 

 interpreted in some manner. Almost every insect which has sound 

 receiving mechanisms also has sound producing (stridulating) organs. 

 In the common locust there are two types of stridulation. When at rest, 

 certain species draw the femoral joint of the hind leg across a specialized 

 vein of the wing cover to produce sound. When flying, they produce a 

 crackling sound by rubbing wings and wing covers together. Tympanic 

 membranes connected by nerves to the nervous system are assumed to 

 be auditory organs. The female mosquito produces a characteristic 

 sound by vibrating her wings 512 times per second. In male mosquitoes 

 the hairs on the antenna are auditory. The hairs are adjusted during 

 flight so that the two plumelike antennae are stimulated equally by the 

 wing sounds produced by the female, thus directing the male toward 

 the female. In the cicada the male has a pair of large, ridged, parch- 

 mentlike drumheads on the first abdominal segment beneath the wings. 

 The drumheads are vibrated by a pair of muscles. A pair of cavities 

 within the body act as resonators for the sounds produced. The female 

 cicada has no sound-producing or sound-receiving apparatus. In the 

 katydid the stridulating organs consist of a rough file and a scraper on 

 the wing covers. The sound-receiving apparatus consists of a series of 

 tympanic chambers with membranous tympana. The latter pick up the 

 sound vibrations (chirp) and transmit them to the nervous system. The 

 chambers intensify the sounds. The honeybee produces its humming 

 sound by moving its wings 190 times per second. The housefly produces 



