38 EVOLUTION. 



Nebular Hypothesis. 



The nebular hypothesis, suggested by Sweden - 

 borg, Buffon, and Kant, and systematized by 

 Herschel and La Place, assumes the former existence 

 of a vaporous matter, extending beyond the orbit of 

 the farthest planet, which by rotation gradually gained 

 solidity, throwing off rings which broke up into 

 planets and moons, the central mass forming the 

 present sun. The existing solar system is satisfac- 

 torily accounted for by this theory, which is now 

 generally accepted by learned men as the best expla- 

 nation of the universe. All the other systems of 

 stars are supposed to have originated in the same 

 manner. 



The earth being thus accounted for as the result of 

 a natural process, the evolutionist sees that all forms 

 of life upon it may have developed from the simplest 

 cell-form of matter, for he can trace an almost con- 

 tinuous evolution from the plant cell upward, through 

 all the grades of vegetable and animal life, to the 

 highest development — man, thus establishing the 

 unity and connection of all nature. 



Spontaneous Generation, 



Sir William Thomson has suggested that life 

 originated on the earth from germs contained in 

 meteoric stones that fell from inhabited planets. But 

 this idea has not received much support. Haeckel 

 and many others maintain that the first forms of life 



