22 Darwin, and after Darwin. 



equivocal that Mr. Wallace, who is one of our greatest 

 ^authorities on geographical distribution, has laid it 

 down as a general law, applicable to all the depart- 

 ments of organic nature, that, so far as observation 

 can extend, " every species has come into existence 

 coincident both in space and time with a pre-existing 

 and closely allied species." As it appears to me that 

 the significance of these words cannot be increased by 

 any comment upon them, I will here bring this intro- 

 ductory chapter to a close. 



