182 GEOLOGICAL BIOLOGY. 



were predetermined when it began its development. So it is 

 with all organisms. It was this fact, of the perfect repetition 

 of all the essential characters of the ancestors in the new 

 individual, that seemed, in the minds of the early naturalists, 

 so absolutely to fortify the belief in the immutability of 

 species. The slight modifications in unimportant details 

 appeared as mere accidental imperfections of the individual. 

 But it was in these slight variations that Darwin found the 

 secret of evolution. 



