X GIANT FISHES, WHALES AND DOLPHINS 



purely aquatic life, that propel and balance themselves by 

 means of fins, and obtain oxygen for breathing from the air 

 dissolved in the water by means of gills. Thus, such creatures 

 as sponges, jellynshes, crustaceans, shellfish, and even the 

 gigantic squids of the ocean depths, often popularly referred 

 to as " fishes ", are excluded, since they all lack a backbone. 



The main part of the book is divided into two sections, one 

 devoted to whales and dolphins, the other to fishes, and the 

 authors are each responsible for one of these sections. Only in 

 the case of the introductory chapter has actual collaboration 

 been attempted. At the same time, every effort has been 

 made to ensure that the method of treatment of the various 

 forms and the arrangement of the subject-matter is roughly 

 the same throughout. 



Zoologically speaking, the two groups of aquatic animals 

 dealt with in the separate sections of the book are vastly 

 different in size and importance. In classifying the great 

 group of Vertebrates, the zoologist divides this into a number 

 of primary divisions or classes. These classes are : Lampreys 

 and Hag-fishes, etc. (Marsipobranchii) ; Sharks, Rays and 

 Chimaeras (Selachii) ; Bony Fishes (Pisces) ; Frogs, Toads, 

 Newts, Salamanders, etc. (Batrachia) ; Reptiles (Reptilia) ; 

 Birds (Aves) ; and Mammals (Mammalia). The Cetaceans 

 (Whales, Dolphins, Porpoises, etc.) represent one of the Orders 

 into which the class Mammalia is further subdivided, whereas 

 the " fishes " include no less than three classes of Vertebrates. 



The aim of the book is twofold. In the first place, by the 

 provision of simple keys, descriptions and accurate illustrations, 

 it is hoped that the reader may be able to identify any of the 

 whales, dolphins or large fishes that he may be in a position 

 to examine. It is not claimed that these will enable a whale 

 or fish to be recognized when swimming in the sea, although in 

 many cases careful perusal of the descriptions and figures 

 should render this possible. In the second place, the authors 

 have tried tc provide a readable account of the appearance, 

 size, habitat, mode of life, food, breeding habits, economic 

 importance and so on of the various creatures that find a 

 place in the book. They have not hesitated to draw upon the 

 subject-matter of a large number of books and scientific papers 

 not readily available to the general public. 



