34 
THE NATURALIST AND COLLECTOR 
Geographical Distribution of Plants and Animals. 
TRAVELER, journeying-through 
a Estrange country, one in 
which the animals have not been so 
dispersed by civilization as to form an 
uneligible and complicated system, 
is at once struck by the diversity of the 
characteristic animals and plants in¬ 
habiting the different parts of the 
same province; even under the same 
conditions of altitude, climate, moist¬ 
ure etc., widely diversified species are 
represented. Why two places having 
the same climatic conditions have come 
to possess widely different faunas and 
floras, even when separated by no per¬ 
ceptible barriers, is one of the most in¬ 
teresting. yet, withal, one of the most 
difficult problems that science has en¬ 
deavored to explain. 
The most powerful barrier to the 
dispersion of species is the unplastic¬ 
ity of parts The main reason why 
animals do not readily adapt them¬ 
selves to different degrees of moisture, 
heat and cold, is that their deficate 
organisms are not sufficiently plastic 
to readily admit of a change. Man, 
and his ever faithful friend, the dog, 
are the only animals that can readily 
adapt themselves to extreme degrees 
of temperature. The more highly de¬ 
veloped the man is, the more readily 
does he adapt himself to climatic con¬ 
ditions. A savage is more susceptible 
to a change in temperature and exhib¬ 
its greater discomforture when out of 
his native region, than do the higher 
civilized races of men. The longer an 
animal has been domesticated, the 
more readily can it adapt itself to 
changes. The dog is not as susceptible 
to and is not as greatly influenced by a 
change as are the various animals 
which have not been as long in a state 
of domestication. 
The conditions under which an an¬ 
imal lives while domesticated, as well 
as its food, etc., produces an elasticity 
of parts, enabling them to undergo a 
series of changes without being ser¬ 
iously affected. This condition, al¬ 
though at first very slight and admit¬ 
ting of but slight changes, has been 
transmitted according to the laws of 
heredity, strengthened in each suc¬ 
cessive generation, till after many cen¬ 
turies it has become a positive inher¬ 
itance. 
The first question in regard to the 
distribution of plants and animals, 
would naturally be concerning the 
barriers to their dispersion. 
The most effectual barrier to the 
free migration or dispersal of animals 
is naturally that presented by the 
oceans. The animals on opposite sides 
of the Pacific are entirely different; 
while in but a few cases are two 
identical species found on opposite sides 
of any ocean, these few, no doubt hav¬ 
ing been brought over in vessels at a 
comparative recent date. Difference 
in climate also presents a great barrier. 
The animals inhabiting the tropics be¬ 
ing totally unlike those of the frigid 
regions. Mountains frequently act as 
a barrier; the difference in the humid¬ 
ity of the air restraining animals of 
delicate organisms from crossing their 
summits. The majority of the animals 
between the Rockies and the Sierra 
Nevada differ from those of the prai¬ 
rie lands east of the Rocky mountains. 
Civilization has proven a great barrier 
as well as a means of dispersal. An¬ 
imals of solitary and secluded habits 
have been compelled to move westward 
