The real affinities of all organic beings, in contradistinction to their adaptive resemblances, are due to inheritance or community of descent.

The Natural System is a genealogical arrangement, with the acquired grades of difference, marked by the terms, varieties, species, genera, families, etc.

; and we have to discover the lines of descent by the most permanent characters, whatever they may be, and of however slight vital importance.

The similar framework of bones in the hand of a man, wing of a bat, fin of the porpoise, and leg of the horse--the same number of vertebrae forming the neck of the giraffe and of the elephant--and innumerable other such facts, at once explain themselves on the theory of descent with slow and slight successive modifications.