general similarities in the hypothalamic mechanisms for these responses 

 in many species. The following types of studies should lead to valuable 

 contributions in this field: electrical stimulation of the hypothalamus 

 in free-swimming sharks; study of the effect of lesions of the hypothalamus 

 and related areas on feeding and attack; and analysis of the detailed 

 anatomy, electrophysiology and pharmacology of the shark hypothalamus and 

 its related areas. 



b. Orientation Mechanisms 



In all animals, the capability to perform movements whose direction 

 is related to environmental cues is of paramount significance and will be 

 referred to as "orientation" in this statement (Schone, 1973) . In fishes, 

 its survival value is obvious in many critical biological functions: the 

 localization of prey or predator, mate and spawning site, advantageous or 

 noxious physical and/or chemical conditions. In all these circumstances, 

 locomotion must be directed or oriented in relation to environmental stim- 

 uli, singly or in combinations, perceived through sensory mechanisms, and 

 evaluated by the central nervous system. In spite of the impressive 

 array of functions which directly depends on the capability of orientation, 

 the mechanisms by which physical and chemical cues are used in directing 

 locomotion are insufficiently known at best in the higher fishes and 

 almost entirely speculative in the elasmobranchs. 



The available information regarding sharks refers almost exclusively 

 to the localization of food sources and the role of chemical and acoustic 

 cues in orientation (Parker, 1910; Sheldon, 1911; Parker and Sheldon, 1913; 

 Aronov, 1959; Teichmann and Teichmann, 1959; Pavlov, 1962; Tester, 1963; 

 Hobson, 1963; Kleerekoper, 1963; Myrberg et al. , 1969 and 1972; Nelson and 

 Johnson, 1972) . The effectiveness of orientation through chemoreception 

 in the absence of other directional cues has been a topic of much specu- 

 lation and some descriptive and quantitative experimentation (Kleerekoper, 

 1962, 1965, 1967 a and b, 1969; Mathewson and Hodgson, 1972). These 

 investigations have indicated that accurate localization of a chemical cue 

 by elasmobranchs is affected by and dependant on water flow. A recent 

 laboratory study, employing electronic techniques and time series analyses 

 of various locomotor variables, monitored during many hours, quantified 

 the relationship between chemical cue and water flow in the orientation of 

 Ginglymostoma cirratum (Kleerekoper e_t a_l. , 1975) . It was established 

 that accurate localization of a chemical cue was dependent on flow of the 

 medium. In the absence of such flow, localization became generalized. 



Elegant experiments on electrical orientation have been performed in 

 both sharks ( Scyliorhinus , Triakis) and rays ( Raja , Platyrhinoidis ) . Well- 

 aimed feeding responses were evoked and directed by the bioelectric fields 

 that prey (e.g. the flatfish Pleuronectes ) produce (Kalmijn, 1966, 1971, 

 1972). At short range (a few inches), electrical cues appeared to dominate 

 chemical cues. The acute electric sense of sharks and rays may well play 

 an important part in the animal's daily life (Kalmijn, 1974). 



Orientation in sharks by acoustical cues has been studied in recent 

 years by various workers (Nelson and Gruber, 1963; Banner, 1968, 1972; 

 Myrberg, 1969; Myrberg et al. , 1969, 1972; Nelson and Johnson, 1970, 1972) 

 who have provided evidence for the possible role of low frequency sounds 

 in the localization of prey by these animals. Attempts to demonstrate 



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