336 THE MULES. 



we must not expect assent to be readily granted 

 to others not amenable to similar demonstration. 

 Where we have as yet only a very small stock of 

 experiments to guide us, where a multiplicity of 

 distant and minor considerations must be weighed 

 against each other, conclusions that appeared legiti- 

 mate become questionable ; and though the human 

 mind often continues to uphold them with more 

 tenacity than judgment, they are defended with 

 less and less ardour, and finally are surrendered, 

 like all other unprofitable prejudices. We might 

 go on to show how little we are acquainted with 

 the resources of Nature in the history of insects, in 

 the laws affecting the life of those low orders of ex- 

 istence which pass into vegetable and stony forms ; 

 we might ask what is known of the microscopic and 

 ephemeral beings which spring into vitality and 

 perish within the few hours of a solar day, and are 

 not again reproduced until a space of time is elapsed 

 indefinite or exceeding three hundred fold the dura- 

 tion of the appointed limits of animation ; we might 

 point to surmised animals and their germs reposing 

 in the depths of earth, slumbering perhaps in a niglit 

 of ages, to be called at some future moment into 

 their day of active being ! Finally, when we every- 

 where observe organic remains in evidence of an 

 infinity of lost animal forms, of destroyed families 

 and genera and species that once were quickened 

 by the irritabilities of life, once fulfilled a design 

 and accomplished the tasks assigned them, we 

 surely, while the plastic power is undeniable in all 



