4 
THE KILIMA-NJAP 0 EXPEDITION. 
the snow-line. In all cases lofty ranges lying in little- 
known regions are interesting to students of natural 
history. Isolated mountains of great height are often 
like oceanic islands, and serve as a refuge and a last 
abiding-place for low types or peculiar forms, which in 
larger and more densely-populated areas find the 
competition too keen, and are extinguished in the 
struggle for life. Or, it may be, some species or genus, 
originally of a generalized type, becomes by various 
circumstances the inhabitant of an alpine range or a 
sea-girt island, and being thus removed and protected 
from the natural checks to its peculiar development 
offered by the contemporaneous evolution of its fellows, 
may, as it were, run riot in the absence of rivalry, and 
assume very eccentric and singular forms. Thus we 
can imagine that a pigeon something like the modern 
didunculus of the South Sea Islands once arrived in 
Mauritius, having perhaps hitherto had to contend 
with the usual dangers which naturally menace the 
existence of a meek-spirited, plump bird that is good 
to eat. But this pigeon, either chancing on Mauritius 
in the course of its long flights, or dwelling on the 
island at a date wdien its connection with a pre-existing 
continent was being severed, found itself in singularly 
favourable circumstances, plenty to eat and nothing to 
attack it—no animals of prey being left on the island. 
So in the course of time, no longer obliged to fly from 
foes or take long journeys in search of food, this 
pigeon became a dodo, huge, fat, and inert, with atro¬ 
phied and useless pinions. Again, on the mountain- 
ranges of Sumatra, of Japan, of North America, also 
on the Alps of Europe, dwell queer, old-fashioned 
ruminants — goat-antelopes, capricorns, chamois — 
which would have long since perished in the fierce, 
