Foreword 



Jtor some years I have been investigating the functional anatomy of 

 mammals speciaHzed for particular modes of progression and endeavor- 

 ing to correlate the facts discovered with their morphology and habits. 

 I have already published several papers of a technical nature on the 

 anatomy of aquatic mammals and the present book is the result of these 

 studies. My endeavor is to present the subject in an essentially non- 

 technical manner, for it is believed that it is of sufficient interest to 

 appeal to a reading public which is larger than that contained in the 

 anatomical or even the purely mammalian field. Partly for this reason 

 lengthy and tedious descriptions and impressive array of data have 

 been omitted. 



The subject of aquatic adaptation in mammals is somewhat peculiar 

 in that there are numerous points which are difficult or impossible of 

 thoroughly conclusive investigation. Habits are at times extremely 

 hard to study and many of the specializations are of such a character 

 that there are no intermediate stages with which they can properly be 

 compared. As a result there has been advanced a truly appalling list 

 of improperly founded theories in attempted explanation of these points. 

 This, however, has perhaps been justified for the reason that only by 

 this means can much progress be made. Many of the specializations 

 are so unusual that in order finally to gain an understanding of them 

 it is first necessary to have a variety of plausible theories from which to 

 work. 



The present contribution is far from the final word on the subject. 

 I believe that I have herewith shown that some of the theories so far 

 tentatively accepted are really untenable, and I have advanced others 

 that to me seem better founded, but some of my readers will justifiably 

 hold contrary opinions, for in morphological interpretations there is 

 invariably produced some chaff with the wheat and further discoveries 

 will surely oblige some revision. In fact I am constantly revising my 

 own beliefs as my knowledge of conditions increases. I have endeavored 

 to evaluate every hypothesis that seemed to hold merit. In attempting 

 to arrive at the proper explanation of some detail I have frequently ad- 

 vanced two or more essentially diverse theories, possibly without in my 

 own mind accepting either of them, but discussing them pro and con 



