PREFACE 



Each year many young biologists make an excursion to the sea. not on 

 idle pleasure bent but for the purpose of studying and investigating marine 

 organisms. For some of these visitors it is perhaps their first actual experi- 

 ence of marine animals in their natural environment, and they will be 

 captivated but bewildered by the multiplicity of life and by the diversity 

 of biological adaptations which they will encounter. It is for these young 

 men and women and for undergraduates specializing in marine zoology 

 that this book has been written, but it is hoped that lecturers and investiga- 

 tors in other fields may find some diversion, if not actual instruction, in 

 the following chapters. 



This book is concerned with the comparative physiology of marine 

 animals, and a knowledge of comparative morphology and general biology 

 has been presumed on the part of the reader. There are limited excursions 

 into allied fields of animal behaviour and ecology, when these can be 

 related to the main theme. In the pages which follow I have tried to show 

 some of the manifold ways in which marine animals, from all kinds of 

 environments, have been able to maintain themselves in the face of hostile 

 physical conditions and severe biotic competition. Whenever possible, at 

 the risk of prolixity, T have cited specific examples in the belief that the 

 functioning and adjustments of each animal deserve particular considera- 

 tion, as revealing how it has managed to solve certain problems of existence. 



Only animals belonging to the marine environment are considered. 

 Probably no apology is needed for this, since the ocean forms a remarkably 

 stable and uniformly graded environment, with far less range of variation 

 than that encountered on land or in fresh water. I have given some con- 

 sideration to problems of littoral and estuarine ecology at the transition 

 between sea, land and fresh water, and of animal associations, when these 

 present features of particular interest to the marine zoologist. Of course, 

 the great majority of examples are taken from littoral and inshore species, 

 for these are the ones most readily available and therefore most thoroughly 

 investigated. 



This book has been in preparation for six years, and during that time 

 many aspects have received extensive treatment elsewhere. Full biblio- 

 graphies of earlier work in comparative physiology are now available and 

 I have therefore confined myself principally to quoting works of the past 

 two decades, including sources in which extensive reference lists may be 

 found. Whenever possible I have attempted to use the presently accepted 

 scientific name for each species mentioned, but there are undoubtedly 

 many instances in which this goal has not been achieved. All measurements 

 are given in the c.g.s. system. 



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