i THE INTRODUCTION OF NEW SPECIES 19 



not materially opposed to any of them. It also claims a 

 superiority over previous hypotheses, on the ground that it 

 not merely explains, but necessitates what exists. Granted 

 the law, and many of the most important facts in Nature 

 could not have been otherwise, but are almost as necessary 

 deductions from it as are the elliptic orbits of the planets 

 from the law of gravitation. 



