COMPARATIVE ANATOMY 



INTRODUCTION 



It is necessary, even in the study of Natural Science, to have 

 something of the nature of a creed, an abiding behef in some 

 fixed principle, which may regulate and give coherence to the 

 mass of information and ideas which we accumulate in the 

 course of our studies. Without such a behef to guide us 

 we embark on our journey of investigation without rudder, 

 compass, or pilot. 



In those sciences which occupy themselves with the explana- 

 tion of the existing order of things on the earth, the funda- 

 mental beliefs are, firstly, that the course of Nature has been 

 uniform — that is to say, that in past times the same forces have 

 operated, possibly with varying intensities, but always in the 

 same manner as those which are in operation to-day. Secondly, 

 that that which is, is the outcome of that which has been, and 

 is the forerunner of that which will be. The history of the 

 world and its inhabitants presents itself to our imaginations as 

 an unbroken series of successive states, each differing somewhat 

 from its predecessor and successor, but as truly derived from 

 its predecessor as the child is derived from its parent, and 

 as truly the antecedent of its successor as the parent is the 

 antecedent of the child. This belief is what we express by the 

 word Evolution. 



The Science of Comparative Anatomy is founded on these 

 principles. It believes that living things, ever since their first 

 appearance on the earth, have been essentially the same as 

 they are now, and that the concourse of living animals which 

 now peoples the globe is the result of a long-continued process 

 of evolution, reaching far back into geological time. The as- 

 semblage of animals at any given period of the earth's history, 

 with all its diversities of form, habit, and structure, was directly 

 descended from the somewhat different assemblage of the pre- 

 ceding period, and, in its turn, gives rise to the assemblage 

 of the period next following, just as one generation of men 



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