1 30 EVOL UTION AND NA TURAL THEOL G Y. 



atmosphere of a planet, they are generally 

 heated to redness, and entirely dissipated ; while 

 if they reach the surface of the ground at all, 

 they are generally split into fragments in their 

 descent, and are always too hot or too cold to 

 be touched outside, and if broken open imme- 

 diately, are often if not always too cold to be 

 touched inside, no matter what may be their 

 external temperature. Surely these violent 

 alternations of temperature would be sufficient 

 to destroy the vitality, if not the very existence 

 of any conceivable germ ! JSFor, as we have 

 already mentioned, could such adventitiously 

 introduced germs develop themselves, except 

 upon a world already prepared for their re- 

 ception. 



Moreover the organic life of the earth shows 

 no signs of having been derived from any 

 extraneous source. On the contrary, all our 

 knowledge of geology tends to prove that terres- 

 trial organisms, so far as know them, have run 

 a definite qourse, and that their origin is to all 

 appearance to be sought for in this world alone. 

 It is probable that the inhabitants of every 

 planet are physically complete in themselves, up 

 to the stage of development to which they have 



