INTRODUCTION 13 



parison of the anatomy and physiology of all animals, 

 existing and extinct, to discover the fundamental like- 

 ness underneath the superficial differences, and to trace 

 the adaptation of organs to the habits and spheres of 

 life. It is this comparative science which has led to 

 such grand generalizations as the unity of structure 

 amidst the diversity of form in the animal creation, 

 and by revealing the degrees of affinity between species 

 has enabled us to classify them in natural groups, and 

 thus laid the foundation of Systematic Zoology. When 

 the study of structure is limited to a particular class or 

 species of animals, or to a particular organ or part, 

 monographic sciences are created, as Ornithotomy, or 

 anatomy of birds ; Osteology, or the science of bones ; 

 and Odontography, or the natural history of teeth. 



Systematic Zoology is the classification or grouping of 

 animals according to their structural and developmental 

 relations. The systematic knowledge of the several 

 classes, as Insects, Reptiles, and Birds, has given rise 

 to subordinate sciences, like Entomology, Herpetology, or 

 Ornithology -, 1 * 



Distributive Zoology is the knowledge of the successive 

 appearance of animals in the order of time (Paleontology 

 in part), and of the geographical and physical distribu- 

 tion of animals, living or extinct, over the surface of the 

 earth. 



Theoretical Zoology includes those provisional modes of 

 grouping facts and interpreting them, which still stand 

 waiting at the gate of science. They may be true, but 

 we can not say that they are true. The evidence is 

 incomplete. Such are the theories which attempt to 

 explain the origin of life and the origin of species. 



Suppose we wish to understand all about the horse. 

 Our first object is to study its structure. The whole 



* See Notes at the end of the volume. 



