110 HAECKEL 



brought the question of species to the front once 

 more. 



It was impossible to retreat simply to Linn6*s 

 position. Lyell by no means denied Cuvier's 

 various periods in the earth's development as such. 

 He believed, moreover, that the plant and animal 

 populations were different in these epochs. When 

 the forests flourished which have formed the mass 

 of our coal-measures there were no ichthyosauri; 

 when the ichthyosauri came there were no longer 

 any carboniferous forests ; with the ichthyosauri 

 there were no megatheria, and the last ichthyo- 

 saurus was extinct before the megatheria arrived. 

 All that Lyell rejected was the great divine cata- 

 strophes. But when these were abandoned, it was 

 no longer possible to attribute the ^'end" of the 

 extinct species to a divine act. We were faced 

 with the slow and natural conversion of terrestrial 

 things in the course of endless ages. 



Species must have been liable to be destroyed 

 by purely natural causes. The catastrophes were 

 abandoned, yet species had been destroyed. And 

 when that was granted — it was the devil's little 

 finger — a further conclusion was inevitable. If 

 species have died out slowly and naturally in 

 the history of the earth, and new species have 

 made their appearance at the same time, may not 

 these new species have arisen slowly and naturally ? 

 Suppose these simple and purely natural causes, 

 that had brought about the extinction of certain 

 species, had been for others the very starting-point 

 of development ? In one word : if the extinction 



