nr LECTURES ON EVOLUTION 55 



the existing distribution of mountains and plains, 

 of rivers and seas, would show itself to be the 

 product of a slow process of natural change 

 operating upon more and more widely different 

 antecedent conditions of the mineral frame-work 

 of the earth ; until, at length, in place of that 

 framework, he would behold only a vast nebulous 

 mass, representing the constituents of the 

 sun and of the planetary bodies. Preceding the 

 forms of life which now exist, our observer 

 would see animals and plants, not identical with 

 them, but like them, increasing their differences 

 with their antiquity and, at the same time, 

 becoming simpler and simpler ; until, finally, the 

 world of life would present nothing but that un- 

 differentiated protoplasmic matter which, so far 

 as our present knowledge goes, is the common 

 foundation of all vital activity. 



The hypothesis of evolution supposes that in all 

 this vast progression there would be no breach of 

 continuity, no point at which we could say " This 

 is a natural process," and " This is not a natural 

 process ; " but that the whole might be compared 

 to that wonderful operation of development which 

 may be seen going on every day under our eyes, in 

 virtue of which there arises, out of the semi-fluid 

 comparatively homogeneous substance which we 

 call an egg, the complicated organisation of one of 

 the higher animals. That, -in a few words, is what 

 is meant by the hypothesis of evolution, 



