As far as we are aware, this is the first attempt to cover the com­ parative physiology of the pancreatic islets in a monograph. The topics discussed would probably have sufficed to fill about half a dozen monographs, a matter that becomes obvious from a look at the Contents. Hence, we have tried to present the ma­ terial more in the form of a digest, to emphasize evolutionary perspectives, to point out critical issues, and to identify challenging topics for future research. This approach required an arbitrary reduction of the num­ ber of references, and we therefore join the chorus of recent authors who beg their colleagues for understanding if some of their publications do not appear in the bibliography. Keeping up with the current literature was like fighting one of those monsters that grow a couple of new heads for each one that is cut off. Nevertheless, we hope that we have covered most of the key publications up to the autumn of 1986. We gratefully acknowledge the advice of many colleagues, and in particular the invaluable criticisms of Robert L. Hazelwood and Erika Plisetskaya. Special thanks are due to the series editor, Donald S. Farner, for his patience and guidance, both of which were fresh proof of his legendary diplomatic skills. Finally, we wish to thank Dr. D. Czeschlik and his staff at the Springer Verlag for their patience and support. Philadelphia, PA AUGUST EpPLE Greenville, NC JACK E. BRINN September 1987 v Contents Chapter 1. Introduction .......................... .