Scyliorhinus canicula , and the ray, Raja clavata , as sensitive electrical 

 receptors, used to detect minute electric fields as discussed in greater 

 detail in the next section. Orientation to such fields produced by prey 

 has been demonstrated in the laboratory (Dijkgraaf and Kalmijn, 1962, 

 1963; Kalmijn, 1966, 1971, 1972) and though the distance over which this 

 modality operates is apparently quite limited, its extreme sensitivity 

 (0.01 uv/cm) strongly indicates a critical role in prey detection. 

 Speculation has also brought forth the possibility that such sensitivity 

 could aid in navigation or obstacle avoidance in turbid water based on 

 the awareness of changes in the earth's magnetic field (Kalmijn, 1972, 

 1973, 1974). Although these findings certainly do not rule out the 

 possibility of a multi-functional role for the ampullae of Lorenzini in 

 elasmobranch fishes, it is obvious that this modality should be examined 

 in additional species and the phenomenon of electroreception be examined 

 by extensive field investigations, when methodology permits. 



PART B. STUDIES OF SYSTEMS AND ORGANS 



A quick tally of physiological papers in the last several symposia on 

 shark research reveals especially heavy representation of studies in the 

 areas of neurobiology and of osmoregulation. Thus, our emphasis here 

 upon those same areas may reflect the continuing major thrusts of physio- 

 logical research on sharks. The perspectives which follow are organized 

 around the various functions involved, with suggestions of promising areas 

 of future research in each section. 



1. Visual System 



This report covers that modality whose adequate stimulus is photic 

 energy and whose function is to detect and transform spatial-temporal 

 photic information to a frequency modulated neural signal which eventually 

 informs the organism about its external environment. The elasmobranchs 

 possess such a system which fits the general vertebrate plan. This system, 

 however, has become uniquely adapted to the individual behavioral, physio- 

 logical and environmental requirements of the animal it serves. These 

 visual adaptations are so sophisticated that one gets the impression that 

 vision must play an important role in the lives of some, if not all, 

 sharks. 



Tinbergen (1952)has correctly pointed out that the first task in 

 investigating the behavior of an animal is a careful study of its sensory 

 capacities. Such studies, typically involving psychophysics and neuro- 

 physiology not only provide data on the physiological mechanisms subserving 

 a particular modality, but give some understanding of properties of the 

 organism's physical world. Clearly, each animal has its own "Merkwelt" 

 or perceptual world which frequently is very different from our own. Thus, 

 in observing an animal it must be clearly understood that certain stimuli 

 can influence, indeed, release behavior and, equally important, other 

 stimuli can never affect the animal's activities. It is for these reasons 

 that the sensory systems of sharks are being studied in both laboratory 

 and field. 



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