CHAPTER: TI 
THE CHORUS OF MAN'S STAGE 
In most plays the principal actors are assisted by a large 
group of minor characters and attendants, whose parts, 
though less conspicuous, are vital to the drama. It is so 
in nature. Though man dominates creation, his happi- 
ness and even his very existence depend on humbler 
creatures. Nor are they all his friends or the friends of 
his friends. Powerful as he is, man requires the full use of 
all his mental superiority to hold his own against the 
competition of the insects and microscopic enemies which 
threaten his life. 
Man has not always held the stage. Long before his 
entrance, race after race of creatures developed, came to 
the zenith of their power, and gave way in turn to others. 
Perhaps it will be so with man. 
The almost interminable march of life as read in the 
imperfect record of the rocks has presented six especially 
interesting eras, which may be designated as, first, the era 
of the simplest life forms; second, the reign of the inver- 
tebrates; third, the period in which vertebrates, exempli- 
fied by the fishes, made their appearance; fourth, the 
heroic age of vegetation; fifth, the age of reptiles; and 
sixth, the age of mammals, culminating in man. 
The first era embraces the dawn of life. Its duration 
probably is to be reckoned in hundreds of millions of 
years and is at least equal in length to all succeeding 
time. Partly by reason of the vicissitudes of the ages 
which lie between that period and ours, partly because 
its strata have not been thoroughly explored, and more 
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