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formed after considerable diffusion of the earlier types of life 

 had taken place. 



The brilliant researches of Semper, Pilsbry, and others 

 into the organisation of the Mollusca, enable us to indicate 

 the probably true evolutionary area of the chief types of structure, 

 not only of special genera, but of other more important groups, 

 and to map out the probable routes by which the earth has 

 become populated, for although evolution, in a lesser degree, 

 is a characteristic of every region, the theatre of the evolution 

 of the great groups of all forms of life appears to have been 

 much more restricted, and a consideration of all the circum- 

 stances inclines one to the belief in a chief or predominant 

 evolutionary area, in which have arisen the more important 

 types of structure at present inhabiting the globe. The evolu- 

 tionary area of the chief types of terrestrial life is the Palaearctic 

 region, but it is in North Central Europe that the originating 

 force is most strongly exercised, the species or groups arising 

 there being more highly endowed and better qualified to succeed 

 in the life-struggle than the organisms that may have preceded 

 them or may have arisen elsewhere, leading us to expect what 

 has actually occurred, that the species of the European region 

 (PI. VI, fig. i), being naturally superior to all their competitors, 

 were bound eventually, as they have done, to overwhelm and 

 extirpate the evolutionary products of every other country, and 

 to multiply and spread, while improved races or species would 

 continue to arise at the theatre of greatest evolutionary activity, 

 gradually dispossessing their predecessors and driving them 

 farther and farther afield, a process which would be repeated 

 and continued on the advent of each new and improved species 

 or group. 



In this way we have throughout the globe the most highly 

 organised and predominant groups or species (PI. VI, fig. 2) 

 inhabiting the most active evolutionary district, with a gradual 

 diminution of dominating power as we proceed therefrom : thus 

 we have constituted a Chronological Series, or Index to the 

 relative antiquity of the different groups, by the geographical 

 position they occupy in relation to the area from which they 

 emanated, and the farther removed any country or area is 

 from the assumed creative centre, the more ancient and primi- 



