It is an old and trite saying that a preface is written last, placed first and read least. It may also be an explanation or justification for what follows, especially if the author feels that the reader may not agree with him . This is thus, something of an apologia. When I first agreed to write this book, I felt that it was to be directed principally towards the endocrine system of vertebrates especially asthere were availablesome excellent accounts of their osmoregulation. However, it was soon apparent to me that in order to appreciate the role of the endocrines one must strongly emphasize non-endocrine functions involved in the regulation of the animals water and salt balance. In addition several years have elapsed since a full account of vertebrate osmoregulation has been given. I have thus felt free to take an overall look at the animals water and salt metabolism, but have especially emphasized more recent contributions. Possibly the book should now be called ''Osmoregulation and the Endocrines''.
