This book is not a conventional review of diving physiology. The
coverage of the literature has been selective rather than en-
compassing, the emphasis has been on field studies rather than
laboratory investigations, and the dive responses described are often
discussed from the perspective of some of the flaws or weaknesses in the
conclusions. Some of these points are of more historical interest to
note how our concepts have evolved as we learn more about behavior and
responses to natural diving in contrast to forced submersions in the
laboratory. As a result there is a degree of evaluation of some
experiments on my part that may seem obvious or controversial to the
specialist. I have followed this planat times in order to aid the
reader, who I hope is often an untergraduate or graduate stu- dent, the
nonspecialist, and the layman, in appreciating to some degree the level
of dissatisfaction or skepticism about certain areas of research in
diving physiology. In view of historical boundaries in vertebrate
biology, the subject is of broad enough importance to catch the interest
of a wide audience of readers if I have done my job well. For ex- ample,
of the major epochal transitions or events there have been in vertebrate
history, three come immediately to mind: (1) The transition from aquatic
to aerial respiration which ultimately led to a broad occupation of
terrestrial habitats. (2) The development of endothermy.