142 EVOLUTION OF LIFE. 
oceans,—there being no obstacle to their free dispersion. 
The relation of the living animals to those found fossil in 
the same countries is very significant in this respect, the 
Apteryx of New Zealand representing the gigantic Dinor- 
nis, the Armadillo and Sloth the extinct Glyptodon and 
Megatherium. Further, in reference to Geographical Dis- 
tribution, the fact of the plants and animals of islands being 
like those of the nearest island or mainland is as important 
to the Geologist as to the Botanist and Zoologist. Thus, 
Mr. Wallace explains the similarity of the plants and 
animals of Sumatra, Java, Borneo, etc. to those of southern 
Asia by suppbsing that these islands once formed part 
of that continent, being connected with it by Malacca; 
while the Celebes, Moluccas, New Guinea, resembling in 
their flora and fauna Australia, are regarded as forming 
with it another continent, the islands of Bali and Lombok 
indicating the limits of these ancient continents. Mr. 
Wallace says, in crossing over the straits separating these 
islands, "we may pass in two hours from one great divi- 
sion of the earth to another, differing as essentially in their 
animal life as Europe does from America.” The study of 
South America and the Malay Archipelago suggested to 
Messrs. Darwin and Wallace their explanation of the 
Geographical Distribution of plants and animals through 
what Mr. Darwin calls Natural Selection, which may be 
expressed as follows: 
Plants and animals struggle for existence. The imme- 
diate descendants are never absolutely like their parents; 
while remote posterity often differs considerably from them. 
Those plants and animals whose modified organization 
gives them an advantage over those not so favored survive, 
or are naturally selected, and transmit their modifications 
to posterity. 
Let us examine these statements, and try to explain how 
the conclusion follows. 
sas. 
