186 VISION 



populations. Given these restrictions, it is likely that specific solutions to 

 specific problems have been "discovered" independently by different verte- 

 brates in the course of their evolution. Our understanding of these problems 

 and their neural solutions require continued study of the neurobiology, be- 

 havior, and natural history of chondrichthians and other vertebrates. 



ACKNOWLEDGMENTS 



I am very grateful to Dr. Louise Luckenbill-Edds, Dr. Robert Leonard, Dr. 

 Leonard Compagno, and the Steinhart Aquarium for furnishing some of the 

 specimens used in this study. Mr. Daniel Moreno and the staff of the Cleve- 

 land Aquarium devoted considerable time and effort to the initial phase of 

 my shark work, and I thank them again for their many kindnesses. I have 

 also been fortunate to use facilities at the Duke University Marine Labora- 

 tory and at the Marine Field Station (University of Delaware College of 

 Marine Studies), where Dr. Robert Boord and I spend pleasant times investi- 

 gating elasmobranch neurobiology. 



Ms. Alice Hartman, Mr. Ronald Nicholes, and Ms. Elizabeth Reed pre- 

 pared the histology. Art work was done by Mr. Donald Luce and Ms. Susan 

 Sanford. Dr. Timothy Neary and Dr. Milford Wolpoff were of great help to 

 me in calculations for the quantitative portions of this work. Mary Sue 

 Caudle Northcutt assisted in many phases of the research and helped con- 

 siderably in compiling the manuscript. 



I thank the Wistar Institute Press for permission to use Figures 24 and 25, 

 and the American Society of Zoologists for the use of Figures 6, 18 and 19. 

 This work was supported, in part, by grants from the National Institutes of 

 Health (NS11006) and the National Science Foundation (GB-40134). 



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