162 THE GENESIS OF SPECIES. [CHAP. VI. 



period of organic evolution. Finally, the absence or 

 rarity of fossils in the oldest rocks is a point at pre- 

 sent inexplicable, and not to be forgotten or neglected. 



Now all these difficulties are avoided if we admit that 

 new forms of animal life of all degrees of complexity 

 appear from time to time with comparative suddenness, 

 being evolved according to laws in part depending on sur- 

 rounding conditions, in part internal similar to the way 

 in which crystals (and, perhaps from recent researches, 

 the lowest forms of life) build themselves up according 

 to the internal laws of their component substance, and 

 in harmony and correspondence with all environing 

 influences and conditions. 





