viii PREFACE 



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 v/hich 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 

 affinities 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 



