INTRODUCTION 3 



belong to the fishes, and the latter to birds. Yet, on study- 

 ing their structure, we find that, not only do these animals 

 merit a place in the class which they occupy, because they 

 possess the distinctive characters of mammals ; but, still 

 further, their internal structure is analogous to that of man 

 and of the other individuals of this class. 



Notwithstanding this similarity of structure, the whale 

 is not without some points of difference from its neighbours 

 the horse and the dog ; therefore, in order to place each of 

 these animals in a position suitable to it, mammals are 

 divided into secondary groups called orders. The first of 

 these orders includes, under the name primates, man and 

 apes. The latter contain animals which approach birds in 

 certain characters of their organism, forming a link between 

 the latter and mammals. 



We find, in studying the regions of the body in some of the 

 vertebrates, that, while they present differences from the 

 corresponding regions of the human body, they also offer 

 most striking analogies. We can, for example, recognise 

 the upper limb of man in the anterior one of quadrupeds, 

 in the wing of the bat, in the paddle of the seal, etc. It is, 

 so to speak, those variations of a great plan which give 

 such a charm to the study of comparative anatomy. 



The division of classes into orders, which we have just 

 mentioned, being still too general, it was found necessary to 

 establish subdivisions — more and more specialized — to 

 which the names families, genera, species, and varieties were 

 given. 



I — 2 



