118 THE TRANSFORMATIONS OF THE ANIMAL WORLD 



duced new ideas into descriptive natural history, 

 and has assigned to it a more noble aim. But we 

 must not forget that it is at present only a theory, 

 which requires to be proved. I have endeavoured 

 to show what interesting proofs have been brought 

 to its support by palaeontological researches, but 

 I ought not to conceal the great gaps in our demon- 

 strations. Science aspires above all to truth. 

 The more we are convinced of the fragile nature of 

 the bases of our theoretical knowledge, the more 

 should we aim at solidifying them by facts and by 

 further observations." 



Wise advice, which might well be thought over 

 and followed by those palaeontologists with ad- 

 venturous minds, eager to construct, with feverish 

 haste, genealogical trees without end, of which the 

 rotten trunks, according to the picturesque ex- 

 pression of Rutimeyer, beaten down as soon as they 

 are set up, encumber the soil of the forest, and 

 render access more difficult to the progress of the 

 future. 



