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Beer G. Vertebrate Zoology. (1922)

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Vertebrate Zoology

An Introduction To The Comparative Anatomy Embryology And Evolution Of Chordate Animals

By

Sir Gavin Db Beer, M.A., D.Sc., F.R.S.

Director Of The British Museum (Natural History).

Sidgwick And Jackson Limited London September, 1922

Preface

THERE are two methods of teaching Zoology. One method is to deal with a limited number of selected types one by one, and the other is to compare corresponding parts of a number of different animals. Each method has its advantages and its drawbacks. The type method is essential for gaining acquaintance with actual animals, and is of fundamental importance from the fact that it permits of practical study of the complete animals themselves. It cannot be too much emphasised that Zoology is the study of animals, and not the study of books written about them. That being so, it is obviously more convenient to dissect and study one type thoroughly before passing on to the next, than to have a number of ilissections of corresponding portions of several animals all going on at the same time. The ﬁrst two parts of this book are devoted to a study of types carefully selected so as to be of the greatest utility in the interpretation of other forms. Part I deals with the adult structure, and Part II with the modes of development.

While the type method is necessary for a start, it is attended with certain dangers. Too much attention may be paid to the types themselves and too little to the other animals of which they are but only in a general way typical. There is also the danger that “ . . . a multitude of facts overcrowd the memory if they do not lead us to establish principles. . . .” I have sought to remedy this with the help of a comparative treatment of the various organ-systems, which forms the subject of Part III. In this part, the information obtained in Parts I and II is woven into a framework, and other animals of interest are interpolated, so as to present a general view of the organsystems from the evolutionary and functional points of view. By this means, it is possible to mention .the signiﬁcant points of certain animals which are unsuited to be taken as types in themselves. In many cases these interpolated animals are fossils, from the fragmentary knowledge of which it would be impossible to construct a sufficiently instructive type.

The use of this comparative treatment following upon the descriptions of types entails a certain amount of repetition, and this is intentional. Unfamiliar facts, which by themselves may be devoid of any particular interest, acquire an added attractiveness and signiﬁcance when they are introduced under more than one setting.

Lastly, in Part IV the types and comparisons are woven together into a whole, and treated as a history of the chief groups of vertebrate animals. It is hoped that the general nature of the treatment of the characteristic features of vertebrates, and the inclusion of a section dealing with the aﬂinities and evolution of the human race, may not be without interest for the human anatomist.

A few words may be added with regard to the types. They are selected and treated not only for their intrinsic importance, but also as introductions to the next types. The description of each type is therefore to some extent based on previous types. So the dogﬁsh is not only an example of a primitive ﬁsh, but it also provides the material on which the disposition of the arterial arches and cranial nerves may be studied, and the knowledge so obtained is used in the interpretation of all higher types. Similarly, Gadus serves as an introduction to the bones of the skull, and Triton introduces the limb of the land-vertebrate. This must explain what may appear to be a lack of balance in the treatment of certain types.

Apart from the more ordinary dissections and observations which I have been able to make personally, I am indebted for sources of information chiefly to the teaching of the Oxford school of Zoology, and in particular to Professor E. S. Goodrich, F.R.S., whose principles I have largely attempted, however unsuccessfully, to follow. I wish to record my gratitude to him for his general guidance in many matters, and for the facilities which I have enjoyed in the Department of Zoology and Comparative Anatomy of the Oxford University Museum.

On occasion, I have had the privilege of discussing certain matters with Professor G. Elliot Smith, F.R.S., Professor C. Judson Herrick, Professor J. P. Hill , F.R.S., Professor Sir Charles Sherrington, 0.M., F.R.S., Professor W. J. Sollas, F.R.S., Professor A. Thomson, and Professor D. M. S. Watson, F.R.S. To all of them I wish to make due. acknowledgment for the help which their information and advice have afforded me. To my friend and colleague Mr. B. W. regarding my ‘thanks to Professor Julian Huxley, F.R.S., without W :11’l8'tI‘9Si|0ﬂ._ IMGTCSL and persistent encouragement this book would have remained unwritten. It goes without saying that these gentlemen are not responsible for the errors which this book

Book - Vertebrate Zoology 1922

Vertebrate Zoology

Preface

Contents