12 ON THE LAW WHICH HAS REGULATED 
recent mountain elevations, separates faunas and floras 
which scarcely differ more than may be due to climate 
and latitude alone. 
The series of facts alluded to in Proposition (3), 
of closely allied species in rich groups being found 
geographically near each other, is most striking and 
important. Mr. Lovell Reeve has well exemplified it 
in his able and interesting paper on the Distribution 
of the Bulimi. It is also seen in the Humming- 
birds and Toucans, little groups of two or three 
closely allied species being often found in the same 
or closely adjoining districts, as we have had the 
good fortune of personally verifying. Fishes give 
evidence of a similar kind: each great river has 
its peculiar genera, and in more extensive genera 
its groups of closely allied species. But it is the 
same throughout Nature; every class and order of 
animals will contribute similar facts. Hitherto no 
attempt has been made to explain these singular 
phenomena, or to show how they have arisen. Why 
are the genera of Palms and of Orchids in almost 
every case confined to one hemisphere? Why are 
the closely allied species of brown-backed Trogons all 
found in the Hast, and the green-backed in the 
West? Why are the Macaws and the Cockatoos 
similarly restricted? Insects furnish a countless 
number of analogous examples ;—the Gboliathi of 
Africa, the Ornithopteree of the Indian Islands, the 
Heliconide of South America, the Danaide of the 
East, and in all, the most closely allied species found 
