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CHAPTER VII. 



THE EVOLUTION OF ORGANIC TYPES IN TIME. 



The naturalists of last century, and of the earlier part of this century, 

 generally believed that the existing forms of animals and plants had 

 been simultaneously produced by a special act of creation, and that 

 they had not been preceded by pre-existent animals and plants. 

 The occurrence of fossils in the crust of the earth had, it is true, 

 been for long recognised, and had given rise to much learned con- 

 troversy. By some, fossils were looked upon as having been pro- 

 duced by inorganic agencies, and thus as not being really the remains 

 of animals and plants. Others, again, clearly recognised that fossils 

 were truly the remains of organisms, but regarded them as having 

 belonged to animals that had been destroyed in the Noachian 

 deluge. 



At the present day it is universally recognised that our existing 

 animals and plants have been preceded by many antecedent faunae 

 and florae. It is also generally admitted that the existing animals 

 and plants are the modified descendants of older forms of life. The 

 actual beginnings of life upon the earth are still unknown to us, and 

 are likely ever to remain so. We have no reason to think that the 

 most ancient of known fossils belong to the animals which first came 

 into existence, but much reason to come to an opposite conclusion. 

 Palaeontology teaches us that new forms of life have been from time 

 to time introduced upon the earth, and that forms already in exist- 

 ence have become extinct. The laws which have governed this in- 

 troduction of new and disappearance of old life-forms are still imper- 

 fectly known to us, but of the fact of this succession of organic types 

 in time no doubt whatever is possible. It is also quite certain that 

 there has been not only a succession but likewise a progression of or- 

 ganic forms in proceeding from the most ancient of geological periods 

 to the present day. The whole subject of the evolution of life-forms 

 in time involves some of the most profound problems of Palaeontol- 

 ogy, and can be but very briefly glanced at here. The more im- 



