ii.] THE PLANT AND THE ANIMAL 119 



distinguished from the animal by fixity and insensibility, 

 movement and consciousness sleep in it as recollections 

 which may waken. But, beside these normally sleeping 

 recollections, there are others awake and active, just those, 

 namely, whose activity does not obstruct the development 

 of the elementary tendency itself. We may then formulate 

 this law: When a tendency splits up in the course of its 

 development, each of the special tendencies which thus arise 

 tries to preserve and develop everything in the primitive 

 tendency that is not incompatible with the work for which 

 it is specialized. This explains precisely the fact we 

 dwelt on in the preceding chapter, viz., the formation 

 of identical complex mechanisms on independent lines 

 of evolution. Certain deep-seated analogies between 

 the animal and the vegetable have probably no other 

 cause: sexual generation is perhaps only a luxury for 

 the plant, but to the animal it was a necessity, and the 

 plant must have been driven to it by the same impetus 

 which impelled the animal thereto, a primitive, original 

 impetus, anterior to the separation of the two kingdoms. 

 The same may be said of the tendency of the vegetable 

 towards a growing complexity. This tendency is essential 

 to the animal kingdom, ever tormented by the need of 

 more and more extended and effective action. But the 

 vegetable, condemned to fixity and insensibility, exhibits 

 the same tendency only because it received at the outset 

 the same impulsion. Recent experiments show that it 

 varies at random when the period of "mutation" arrives; 

 whereas the animal must have evolved, we believe, in 

 much more definite directions. But we will not dwell 

 further on this original doubling of the modes of life. Let 

 us come to the evolution of animals, in which we are more 

 particularly interested. 



