112 



HYPOTHESIS OF THE DEVELOPMENT 



OF THE 



VEGETABLE AND ANIMAL KINGDOMS. 



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

 ticular 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 passed on, otherwise than by a series of interferences, 

 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 ne- 

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

 to the animal kingdom, the vegetable department of nature, 

 which starts from a common, or at least, contiguous basis, 

 being sure to fall into any system which may be found appli- 

 cable to the other. 



It has already been intimated that the succession of animals 

 throughout the geological eras is generally conformable to 

 the gradation of forms in the animal scale, taking these in 

 broad masses, and allowing for such imperfections in the 

 series as geology itself at once leads us to expect, and partly 



