THE INTRODUCTION OF NEW SPECIES. 5 
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. 
6. Most of the larger and some small groups ex- 
tend through several geological periods. 
7. In each period, however, there are peculiar 
groups, found nowhere else, and extending through 
one or several formations. 
8. Species of one genus, or genera of one family 
occurring in the same geological time are more closely 
allied than those separated in time. 
9. As generally in geography no species or genus 
occurs in two very distant localities without being 
also found in intermediate places, so in geology the 
life of a species or genus has not been interrupted. 
In other words, no group or species has come into 
existence twice. 
10. The following law may be deduced from these 
facts :—EHvery species has come into existence coincident 
both in space and time with a pre-ewisting closely allied 
species. 
This law agrees with, explains and illustrates all 
the facts connected with the following branches of 
