I am still puzzling over such questions as to what is the largest object caught in a spider's web and what are the limitations to building larger webs? Or, what might be the selective forces that have operated on the evolution of aglomerular kidneys that has occurred in a few marine teleost species? These are just a couple of the thought-provoking questions that are posed liberally throughout the latest (4th) edition of Eckert's Animal Physiology that has been revised by Randall, Burggren and French. For those students and teachers who found the earlier editions of this book instructional and a valuable resource, its extensive revision and expansion will be received with enthusiasm. The authors have produced an excellent textbook of animal physiology. The animal kingdom is so diverse, one wonders how such a book can be confined to 700 pages. The aim of the authors has been to carefully elucidate the general physiological principles and physico-chemical laws which govern all forms of animal life and then to illustrate these laws with examples of adaptations drawn from a wide range of organisms. This aim has been largely fulfilled and the authors are to be congratulated on their revision.