196 THE INDUCTIONS OF BIOLOGY. 



case motion and locomotion are superfluous, while in the 

 other case they are necessary: the differences in the degrees 

 of structure being consequences. Eecognizing the locomo- 

 tive powers of minute Algce and the motions of such other 

 AlgcB as Oscillatoria, as well as those movements of leaves 

 and fructifying organs seen in some Phasnogams, we may say, 

 generally, that plants are motionless;, but that they can 

 nevertheless carry on their lives because they are bathed by 

 the required nutriment in the air and in the soil. Contrari- 

 wise, the nutriment animals require is distributed through 

 space in portions : in some cases near one another and in 

 other cases wide apart. Hence motion and locomotion are 

 necessitated; and the implication is that animals must have 

 organs which render them possible. In the first place there 

 must be either limbs or such structures as those which in 

 fish, snakes, and worms move the body along. In the second 

 place, since action implies waste, there must be a set of 

 channels to bring repairing materials to the moving parts. 

 In the third place there must be an alimentary system for 

 taking in and preparing these materials. In the fourth 

 place there must be organs for separating and excreting 

 waste-products. All these appliances must be more highly 

 developed in proportion as the required activity is greater. 

 Then there must be an apparatus for directing the motions 

 and locomotions — a nervous system; and as fast as these 

 become rapid and complex the nervous system must be 

 largely developed, ending in great nervous centres — seats of 

 intelligence by which the activities at large are regulated. 

 Lastly, underlying all the structural contrasts between plants 

 and animals thus originating, there is the chemical contrast; 

 since the necessity for that highly nitrogenous matter of 

 which animals are formed, is entailed by the necessity for 

 rapidly evolving the energy producing motion. So that, 

 strange as it seems, those chemical, physical, and mental 

 characters of animals which so profoundly distinguish them 

 from plants, are all remote results of the circumstance that 

 their food is dispersed instead of being everywhere present. 



