ORGANIC EVOLUTION 349 
uncovered traces of ancient races and have in a measure 
reconstructed their history from fragments, such as coins, 
various objects of art and of household use, together with 
inscriptions on tombs and columns and on those curious little 
bricks which were used for public records and correspond- 
ence. One city having been uncovered, it is found by lifting 
the floors of temples and other buildings, and the pavement 
of public squares, that this city, although very ancient, is 
built upon the ruins of a more ancient one, which in turn 
covers the ruins of one still older. In this way, as many as 
seven successive cities have been found, built one on top of 
the other, and new and unexpected facts regarding ancient 
civilization have been brought to light. We must admit that 
this gives us an imperfect history, with many gaps; but it is 
one that commands our confidence, as being based on facts 
of observation, and not on speculation. 
In like manner the knowledge of the past history of animal 
life is the result of explorations by trained scholars into the 
records of the past. We have remains of ancient life in the 
rocks, and also traces of past conditions in the developing 
stages of animals. ‘These are all more ancient than the 
inscriptions left by the hand of man upon his tombs, his 
temples, and his columns, but nevertheless full of meaning 
if we can only understand them. This historical method of 
investigation applied to the organic world has brought new 
and unexpected views regarding the antiquity of life. 
The Diversity of Living Forms.—Sooner or later the 
question of the derivation of the animals and plants is 
bound to come to the mind of the observer of nature. There 
exist at present more than a million different kinds of 
animals. The waters, the earth, the air teem with life. 
The fishes of the sea are almost innumerable, and in a sin- 
gle order of the insect-world, the beetles, more than 50,000 
species are known and described. Jn addition to living 
