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chalked out. The whole problem, in that case, does in 

 effect resolve itself to this, — Where, and how, are the 

 lines of demarcation to be drawn ? No amount of incon- 

 stancy, provided its limits be fixed, is irreconcilable with 

 the doctrine of specific similitudes. Like the ever- 

 shifting curves which the white foam of the untiring 

 tide describes upon the shore, races may ebb and flow ; 

 but they have their boundaries, in either direction, 

 beyond which they can never pass. And thus in every 

 species we may detect, to a greater or less extent, the 

 emblem of instability and permanence combined : al- 

 though perceived, when inquired into, to be fickle and 

 fluctuating in their component parts, in their general 

 outline they remain steadfast and unaltered, as of old, — 



" Still changing, yet unchanged ; still doom'd to feel 

 Endless mutation, in perpetual rest." 



