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HYPOTHESIS OF THE DEVELOPMENT 



OF THE 



VEGETABLE AND ANIMAL KINGDOMS. 



WE have now seen arguments, of both a general and parti- 

 cular kind, for the simply natural origin of life upon our 

 planet. But, whatever force may be allowed to these argu- 

 ments, no attempt has as yet been made to show how, even if 

 life originated in its first and humblest forms in this manner, 

 it might have passed on, otherwise than by a series of divine 

 acts of a character above or exceptive to the natural order of 

 things, through that double series of higher forms terminating 

 in the dicotyledons and mammalia, which we have seen rising 

 throughout the geological ages, and leaving the earth occupied 

 by its present organisms. 



In now proposing to make such an attempt, I deem it neces- 

 sary, for the sake of simplicity, to confine attention mainly to 

 the animal kingdom, assuming that the vegetable department 

 of nature, which starts from a common, or at least, contiguous 

 basis, is sure to fall into any system which may be found appli- 

 cable to the other. 



It has already been shown, with abundant clearness, that 

 there has been a progression of animal life upon the globe, 

 first, an era of invertebrate animals ; second, a period during 

 which fish were the sole vertebrate form of being ; next, a 

 time when reptiles are seen in addition, but without birds or 

 mammalia ; then a period when these last were added, but 

 without man ; and finally, the present era, in which that 

 master species has existed in supremacy over all. This is a 

 manifest stepping-on from one grade to another, and it is a 

 fact which is only feebly disputed by one or two geologists, on 

 the ground that we know of the absence of the higher animals 



