5i8 SCIENCE PROGRESS 



counterpart of that of a being whose ancestors since the origin 

 of higher animals have led the animal existence. We can hardly 

 admit that without ignoring the importance of agreement and 

 difference, the recognition of which, according to logicians, is 

 the essential part of knowledge. 



There are now in nature two definite phases of the life 

 principle, and at the side of these an elementary indeterminate 

 condition in which they merge. In the latter condition 

 organisms are for the most part microscopic, difficult of analysis, 

 and with few direct connecting links with higher life. 



Evolution, if it has been operative in the world, has turned 

 away from them. The fact that they resemble the cellular units 

 of which the higher animals and, in a lesser degree, the higher 

 plants consist, is no reason for offering them as proofs of unity, 

 especially as they themselves are composite in character. 



Although biology is concerned with both animal and vegetal 

 life, there can be little doubt that its chief interest is with the 

 former, which represents the human phase. At all events there 

 are grounds for thinking that in the pursuit of this science the 

 practice of attaching equal evidential value to examples drawn 

 from both kingdoms is not likely to lead to accurate results. 



Undoubtedly the same elementary substances are operative 

 in both divisions to maintain life ; but the manner and the form 

 in which they are employed are different, and this difference is 

 sufficient to render it inexpedient to regard the primal sub- 

 stance of which plants and animals consist as one and the 

 same thing. 





