EVIDENCES OF EVOLUTION. Ill 



superficial resemblance has entirely disappeared. 

 But although the modifications are so great, they 

 are, nevertheless, just such modifications as would 

 have originated from the fore-limb of some arche- 

 typal form, if this limb had been called upon to 

 perform entirely different functions from those for 

 which it was first adapted, or if the archetypal an- 

 cestor had been introduced to an entirely different 

 environment from the one in which it was originally 

 placed. Analogy, then, is but a superficial resem- 

 blance, whereas, homology is an essential and fun- 

 damental one which, in many cases, can be detected 

 only by experts in comparative anatomy. 



Now, it is precisely the fact of homology of 

 structure, which finds its sole explanation in com- 

 munity of origin, that constitutes one of the strong- 

 est proofs of the theory of Evolution. 



According to the evolutionary theory of natural 

 selection, it is inferred that hereditary characters 

 undergo a change whenever a change will better 

 adapt an organism to changed conditions of life. 

 The whale is again a case in point. From the best 

 evidence obtainable, it is concluded that the ances- 

 tors of whales were land quadrupeds, which became 

 aquatic in their habits. But such a change in their 

 mode of life would necessitate a corresponding 

 change in the functions of various parts and organs. 

 The hind-legs would not be required for purposes 

 of locomotion, and hence they would disappear. 

 The fore-legs would be adapted for swimming, and 

 would, therefore, be transformed into fins or pad- 

 dles. There would also be important changes in 



