THE FACTORS OF ORGANIC EVOLUTION. 757 



for use, they are nerveless and non-vascular, and hence are incapable 

 of undergoing any changes of structure consequent on changes of 

 function. 



Of these few, then, who rejected the belief described by Professor 

 Huxley, and who, espousing the belief in a continuous evolution, had 

 to account for this evolution, it must be said that though the cause 

 assigned was a true cause, yet, even admitting that it operated through 

 successive generations, it left unexplained the greater part of the 

 facts. Obviously the facts that were congruous with the espoused 

 view, monopolized consciousness, and kept out the facts that were in- 

 congruous with it — conspicuous though many of them were. The mis- 

 judgment was not unnatural. Finding it impossible to accept any 

 doctrine which implied a breach in the uniform course of natural cau- 

 sation, and, by implication, accepting as unquestionable the origin and 

 development of all organic forms by accumulated modifications natu- 

 rally caused, that which appeared to explain certain classes of these 

 modifications, was supposed to be capable of explaining the rest : the 

 tendency being to assume that these would eventually be similarly 

 accounted for, though it was not clear how. 



Returning from this parenthetic remark, we are concerned here 

 chiefly to remember that, as said at the outset, there existed thirty 

 years ago, no tenable theory about the genesis of living things. Of 

 the two alternative beliefs, neither would bear critical examination. 



Out of this dead lock we were released — in large measure, though 

 not I believe entirely — by the Origin of Species. That work brought 

 into view a further factor ; or, rather, such factor, recognized as in 

 operation by here and there an observer (as pointed out by Mr. Dar- 

 win in his introduction to the second edition), was by him for the first 

 time seen to have played so immense a part in the genesis of plants 

 and animals. 



Though laying myself open to the charge of telling a thrice-told 

 tale, I feel obliged here to indicate briefly the several great classes of 

 facts which Mr. Darwin's hypothesis explains ; because otherwise that 

 which follows would scarcely be understood. And I feel the less hesi- 

 tation in doing this because the hypothesis which it replaced, not very 

 widely known at any time, has of late so completely dropped into the 

 background, that the majority of readers are scarcely aware of its 

 existence, and do not therefore understand the relation between Mr. 

 Darwin's successful interpretation and the preceding unsuccessful 

 attempt at interpretation. Of these classes of facts, four chief ones 

 may be here distinguished. 



In the first place, such adjustments as those exemplified above are 

 made comprehensible. Though it is inconceivable that a structure 

 like that of the pitcher-plant could have been produced by accumu- 

 lated effects of function on structure ; yet it is conceivable that sue- 



