Osborne and Wersall (1964) and for Carcharhinus by Tester, Kendall and 

 Milisen (1972) . The fine structure of the sensory epithelia of the ear 

 of Raja , including the orientation of the hair cells, has been determined 

 by Lowenstein, Osborne and Wersall (1964). Rauchbach and Arenberg (1972, 

 1973) have demonstrated the use of the scanning EM (SEM) to show the 

 structure of hair cells of the ear of Negraprion and have diagrammed their 

 orientation. J. Corwin (U. of Hawaii graduate student) is presently 

 using both transmission EM (TEM) and SEM to study hair cell orientation 

 in Carcharhinus , particularly with respect to the little known organ, the 

 macula neglecta. EM work should be continued and extended to other genera 

 to provide a firm basis for the interpretation of electrophysiological 

 experiments designed to illucidate how the ear functions in hearing. 

 Other functions of the ear — equilibrium and muscle tonus maintenance — 

 have been worked out for the ray by Lowenstein and Sand (1940a and b) and 

 by Lowenstein and Roberts (1950) . This work should be extended to other 

 sharks . 



There have been many papers in recent years on hearing in sharks, 

 including both tank experiments and studies with free-swimming animals 

 in their natural environment. Although it has been shown that the re- 

 sponse varies with the nature of the sound (continuous, pulsed, train, 

 etc.) and that the response is directional, it has not yet been established 

 whether the stimulus is received through the lateral line, the ear, or 

 both. 



There is need for determining if ahd how the ear participates in 

 hearing. Much can be learned from electrophysiological studies of micro- 

 phonics in various parts of the ear of an immobilized submerged shark, 

 utilizing an underwater sound source as stimulus. There are indications 

 that the macula neglecta may be a main organ of hearing in rays (Lowenstein 

 and Roberts, 1951) and in sharks (Faye, Kendall, Popper and Tester, 1974). 

 Further electrophysiological experiments, with particular attention to this 

 organ, should be undertaken. 



It might be possible to perform diagnostic behavioral experiments to 

 clarify the role of the ear in hearing, subjecting sharks in tanks or in 

 cages in the open environment to underwater sound sources. However it 

 would be difficult to ablate the ear without causing problems in equilib- 

 rium and it would be difficult to ablate the lateralis system because 

 of its complexity. The possibility exists of correlating behavioral and 

 electrophysiological observations by inserting electrodes into the macula 

 neglecta of both ears and telemetering the responses. However, it is 

 difficult to implant electrodes without damaging other parts of the ear 

 and it is difficult to firmly anchor the electrode assembly to the skin. 

 It should be possible to overcome those technological problems in the 

 future. 



4. Other Systems 



a. Central Nervous System 



In sharks, as in any organism, the understanding of an integrated 

 behavior pattern should involve the study of various relevant components 

 of the central nervous system. During the past few decades, such attempts 

 to understand the nature of shark attacks have centered primarily on 



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