THE GEOGRAPHICAL DISTRIBUTION OF ANIMALS. 129 
tances, and the parasites thus introduced attack other spe- 
cies. 
Man, with boundless aspirations and governed in all 
things by an influence within himself, is given a power in 
nature second only to his Creator; with control over physi- 
cal causes, he is governed by no laws of geographical dis- 
tribution, and, traversing the whole earth at his will, he has 
carried, in spite of climatic influences, species from continent 
to continent, and almost from pole to pole. His influence— 
far above all other secondary causes, and uncontrolled by the 
laws imposed upon mere animals—seems only a disturbing 
force among the naturally harmonizing laws of the diffusion 
of life. Many of the changes which man has wrought in the 
distribution of animals are so evident and so universally 
understood, that it is useless to refer to them here, and we 
will allude only to some of those which bear more directly 
upon our understanding of the geographical distribution of 
species. 
_ By changes in the minor physical features of regions, man 
has often adapted them to species of other regions. The 
Cliff-swallow was formerly known only from far west of the 
Mississippi, where there were extensive limestone cliffs for 
it to nest upon; but now that the buildings of man have 
made places for its habitation, it has spread from the Missis- 
sippi all over the Atlantic States.” 
The New Potato-beetle (Doryphora 10-lineata), which 
is so destructive in the West, was long ago known at the base 
of the Rocky Mountains in Colorado, feeding upon a wild 
Species of Solanum peculiar to that region. Civilization, 
pushing westward, at last extended its fields of cultivated 
plants far west of the Mississippi into this region. The po- 
tato (a species of Solanum) was well adapted to feed the 
beetle, and was of course attacked by it. The broad fields 
of cultivated plants were much better fitted for its increase 
than the scattered wild ones, and it rapidly diffused itself 
* A. E. Verrill, Proceedings of the Boston Society of Natural History, Vol. IX, p. 276. 
AMER. NATURALIST, VOL. II. 17 


