the enemy and beat him upon
his own ground. This end is secured in many animals by acquiring horns
or by lengthening certain of the teeth. The horn is a very ancient
instrument of defense. When the reptiles ruled the land horns were not
uncommon. They consisted in those days of hardened scales, which
lengthened and fastened themselves over a core of bone. Such an
old-fashioned instrument, sometimes made of newer materials, still
remains the defense of a number of animals. The rhinoceros has upon
his nose a lengthened projection, which is what might not improperly
be called hair glued into a cone. This enormous horn is a frightful
weapon, both of offense and defense, and, when backed by the terrible
weight of the body of the rhinoceros, it can do as deadly work as
almost any instrument of destruction known to animals below the grade
of man. But, after all, this is an old-fashioned method, and the
rhinoceros is a relic.

Among the carnivorous animals the teeth, which were developed first
chiefly for the tearing of flesh in its consumption, became effective
for their courageous owners. Because these tearing teeth are well
developed in the dog they have come to be known as canine teeth.
Usually where an animal can use its teeth effectively for offense or
defense, it is the canine teeth that are thus modified. The cat has
developed them better than the dog, and one of the cats of a bygone
geological period had canine teeth so magnificently enlarged and so
sharp at the back as to give this frightful creature the name of the
saber-toothed tiger. The long teeth in the upper jaws of the elephant,
commonly known as tusks, are not canine teeth. The elephant has
completely lost his canines. His tusks are his incisors, and they have
developed as have almost no other teeth in the mammals.

These are only a few of the numberless devices nature has evolved for
furthering the success of her children. There are so many others that
to many of us they form almost the chief point of interest in our
study of a new animal, or our closer observation of an old friend.

CHAPTER V

ADAPTATION FOR THE SPECIES

The strife, as we have described it thus far, is a purely selfish
struggle. Every point gained is a point favorable to the welfare of
the individual animal. But nature is uncommonly careless of the
individual unless the advantage gained is also of use to the species
as a whole. Very often the life of an animal ceases when prov