THE EARTH THE ABODE OF LIFE 



brain, or the roots of the hair to name only a 

 few. Thus we see how complicated the structure of 

 animals has become since life first made its appearance 

 on the earth. The cells joined themselves to form tissues ; 

 and the tissues joined themselves to form organs; and 

 these things had to happen before anything like a com- 

 plete animal of the higher type, or even a complete 

 vegetable, made its appearance. Suppose by some great 

 cataclysm, not so great as that which we have imagined 

 in an earlier chapter, but still world-wide in its effects, 

 the whole world should once again be swept by a great 

 outbreak of lava and molten rocks, which of all the living 

 things would leave traces of its existence ? Perhaps a few 

 of the animals with great bones, or the great trees, might 

 leave an impress of themselves in the depths of the over- 

 whelming rocks, just as we can stamp the impress of the 

 skin of our finger-tips on hot sealing-wax ; but it is fairly 

 evident that all the soft-tissued animals and vegetables 

 would disappear entirely and leave not a trace behind 

 certainly no trace that anybody could recognise many 

 millions of years afterwards. It is still more certain that 

 the simplest forms of life, "the unicellular organisms, 11 

 would leave no trace at all. We know that side by side 

 with the complicated organisms that we can see the 

 simplest organisms exist now ; and must have existed at 

 the beginning of life. Yet when we examine the records 

 of living things in the rocks which were formed in the 

 youth of the world, and go back right to the earliest of 

 these forms of life that have ever been discovered, we 

 find that such specimens are all of the rather higher (if 



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