PREFACE 



THE object of this little book is to present a simple 

 account of modern views on the relationships of 

 the chief groups of the animal kingdom, the principal 

 grounds on which the modern classification of these 

 groups may be justified, and an outline of the evi- 

 dence by which some of the main streams of animal 

 evolution can be traced. The science of comparative 

 anatomy with its theoretical super-structure of phy- 

 logeny (the ancestral pedigree of animals) rests so 

 largely upon facts which can only be satisfactorily 

 appreciated by a course of laboratory experience, 

 that it is difficult to present the subject intelligibly 

 to readers who have not already acquired some 

 discipline in zoological science, but, to those who 

 are acquainted with the structure and develop- 

 ment of a few types of animals, it may prove 

 instructive to consider some of the wider problems 

 of animal relationship, and to link up their know- 

 ledge of special types with a more general apprecia- 

 tion of the probable course organic evolution has 

 taken. In tracing out the course of organic evolution 

 the importance of existing primitive types of animals 



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