a Darwin, and after Darwin. 
equivocal that Mr. Wallace, who is one of our greatest 
authorities on geographical distribution, has Jaid 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. 
