DISTRIBUTION. 187 



and more conterminous, the same species had, perhaps, a 

 more extensive range ; but even then there was no uni- 

 versal uniformity of life a thing as incompatible with the 

 habits of the creatures themselves, as uniformity of climate 

 is with the form and motions of the globe. Plant the first 

 germ of life on whatever spot you may, this act of creation 

 has always some relation of fitness to external conditions ; 

 and as universal uniformity of condition is a thing unknown 

 either in time present or in time past, so we may rest assured 

 that universal uniformity of Life was a feature that never 

 entered into the scheme of creation. Tropical and temper- 

 ate, low-lying and elevated, littoral and deep-sea, have ever 

 prevailed as distinctive areas, impressed by different physi- 

 cal conditions, and requiring for their tenancy orders and 

 families equally distinct in their habits and organisation. 

 No doubt certain animals, in consequence of their periodic 

 migrations, have a much wider range than others, but even 

 this is fixed and ascertainable, and these migratory races, at 

 the present day at least, are comparatively few. Applying 

 this rule to the past, we may believe in the migrations of 

 certain extinct races,* but these always within definite 

 limits, and, race for race, each over its own appointed area. 

 From the first to the last, variety and complexity are 

 unmistakably stamped on all created forms ; and this variety 

 manifests itself not only in the structure of the creatures 

 themselves, but in their general fades at successive epochs, 

 as well as over the different areas they were meant to in- 



* The migrations of living animals are comparatively well known ; the 

 migration of extinct races is altogether wrapt in obscurity. And yet we 

 may believe that the mastodons and mammoths had a wide range from 

 south to north, that some of the tertiary birds dipped their wings alike in 

 temperate and arctic waters, and that many of the secondary fishes 

 were, like the salmon and sturgeon, anadromous now frequenting the 

 sea, and now returning to the river under the periodic impulse of repr6- 

 duction. 



