rnishing the best food for cattle, depends largely upon the
visits to the clover-blossoms by wild bees, that accomplish the
fertilization of the flowers by carrying pollen upon their bodies from one
plant to another. Field-mice devour the young in the nests of these bees,
so if there are few field-mice there will be many bees, and consequently
better grazing for the cattle. The number of field-mice will vary
according to the abundance of cats, and so the number of these domestic
animals will exert an influence upon the whole foregoing chain of forms.
But, as Fiske points out, cats are the favorite companions of elderly
spinsters; therefore, if there are many of the latter, there will be more
cats, fewer field-mice, more bees, richer clover fields, and finer cattle!
Each link is real and the whole chain is a characteristic example of the
countless ways that the natural destinies of living things are
interrelated and intertwined.

The reality of such organic interrelationships is revealed with wonderful
clearness in the numerous instances where some disturbing factor has
altered one or another element of the balanced system. The invasion of the
new world by Europeans has directly led to the partial or complete
extinction of the tribes of Indians to whom the land formerly belonged;
they have disappeared almost entirely from our state of New York, together
with the bear and wolf and many other species of animals that formerly
existed here. Wild horses and bison have also vanished before the advances
of civilization and the alteration of their homes. Sometimes the
extermination of one pest has resulted in an increase in the number of
another through human interference with nature's equilibrium. In some of
our Western states, a bounty was offered for the scalps of wolves, so as
to lessen the number of these predatory foes of sheep. But when the wolves
were diminished in number, their wild food-animals, the prairie dogs,
found their lot much bettered, and they have multiplied so rapidly that in
some places they have become even more destructive than the wolves.

One of the most remarkable illustrations is that of the rabbits introduced
into Australia. This island continent was cut off from the surrounding
lands long before the higher mammals evolved in far distant regions, so
that the balance of nature was worked out without reference to animals
like the rabbit. When the first of these were introduced they found a
territory wi