THE INTRODUCTION OF NEW SPECIES 



explaining them all, and giving a direction to new researches. 

 It is about ten years since the idea of such a law suggested 

 itself to the writer of this essay, and he has since taken every 

 opportunity of testing it by all the newly-ascertained facts 

 with which he has become acquainted, or has been able to 

 observe himself. These have all served to convince him of 

 the correctness of his hypothesis. Fully to enter into such a 

 subject would occupy much space, and it is only in con- 

 sequence of some views having been lately promulgated, he 

 believes, in a wrong direction, that he now ventures to present 

 his ideas to the public, with only such obvious illustrations of 

 the arguments and results as occur to him in a place far 

 removed from all means of reference and exact information. 



A Law deduced from well-known Geographical and 



Geological Facts 



The following propositions in Organic Geography and Geo- 

 logy give the main facts on which the hypothesis is founded. 



GKOGRAPHY 



1. Large groups, such as classes and orders, are generally 

 spread over the whole earth, while smaller ones, such as 

 families and genera, are frequently confined to one portion, 

 often to a very limited district. 



2. In widely distributed families the genera are often 

 limited in range ; in widely distributed genera well-marked 

 groups of species are peculiar to each geographical district. 



3. When a group is confined to one district, and is rich in 

 species, it is almost invariably the case that the most closely 

 allied species are found in the same locality or in closely 

 adjoining localities, and that therefore the natural sequence 

 of the species by affinity is also geographical. 



4. In countries of a similar climate, but separated by a 

 wide sea or lofty mountains, the families, genera, and species 

 of the one are often represented by closely allied families, 

 genera, and species peculiar to the other. 



5. The distribution of the organic world in time is very 

 similar to its present distribution in space. 



