I THE INTRODUCTION OF NEW SPECIES 5 
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. 
GEOGRAPHY 
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. 
GEOLOGY 
5. The distribution of the organic world in time is very 
similar to its present distribution in space. 
