relative importance of visual stimuli in the field or the effects of 

 visual stimuli on motivation. This is an area which can bridge the gap 

 between field and laboratory studies and strong consideration should be 

 given to any promising studies of this kind. The main difficulty with 

 this type of investigation involves adequate and reliable methodology. 

 Until this is properly developed, we will still be guessing! 



In summary, knowledge of visual structure and function has rapidly 

 advanced during the past decade: several investigators are applying 

 methods from various disciplines to the study of vision in elasmobranchs. 

 It is now possible to make definitive statements on visual capability in 

 these animals and the picture which emerges is quite different from 

 classical descriptions. Still, as in other phases of elasmobranch biology 

 tangible progress in understanding the visual system in sharks is just 

 beginning. 



2 . The Chemical Senses 



The senses of smell and taste are closely involved with the feeding 

 and attack behavior patterns of sharks. As a consequence, research on 

 these senses of sharks has had a long history. When G.H. Parker published 

 his classic summary of "Smell, Taste, and Allied Senses in the Vertebrates" 

 (1922) there were already many descriptions of the gross morphology of 

 chemical sense organs of sharks. Some of Parker's colleagues had also 

 studied the effects of plugging one nostril in a shark (resulting in 

 circular movements), and attempts were being made to determine the groupings 

 of chemicals which stimulated olfactory, gustatory, and skin chemore- 

 ceptors of sharks. However, the latter studies, on modalities of effective 

 stimuli, were completely inconclusive. 



During most of the intervening half century, research on the chemical 

 senses of sharks has been essentially a refinement of behavioral studies 

 and anatomical investigations which could have been appreciated by Parker 

 and others early in this century. Screening programs for repellents, 

 tests of the attractiveness of various potential food substances, and 

 comparative anatomical studies have dominated the field. A few field 

 studies on feeding behavior of pelagic sharks under natural conditions 

 were made, but mainly on a catch-as-catch-can basis, often in conjunction 

 with natural history expeditions primarily concerned with other objectives. 

 Tester (1963) has given a valuable summary of that phase of the studies on 

 chemical senses of sharks. He noted that there was a need for: 



1) Electrophysical studies of receptor function, already in 

 widespread use on other sensory systems of other animals. 



2) Electro-dissection or other precise techniques of neurosurgery 

 to localize functions within the CNS concerned with the 

 chemical senses. 



3) Tests with pure single chemicals which trigger important 

 patterns of behavior in sharks. 



4) Determination of chemically-mediated patterns of behavior 

 in sharks of other kinds and in other circumstances, beyond 

 the few species and laboratory situations most studied. 



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