ORGANIC EVOLUTION 349 



uncovered traces of ancient races and have in a measure 

 reconstructed their history from fragments, such as coins, 

 various oljjects 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 

 stasres 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 a})plied 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 innumeraljle, and in a sin- 

 gle order of the insect- workl, the beetles, more than 50,000 

 species are known and described. In addition to living 



