EVOLUTION AND ITS CONSEQUENCES. 29 



nutritive fluid is well known to be under the influence of nerve- 

 force. How imagination stimulates secretion is seen in the famil- 

 iar example of the flow of saliva in anticipation of food ; a very 

 different example is the phenomenon of blushing under emotional 

 stimulus. Nevertheless, it is not evident that growth can result 

 with any such facility in a fully grown animal. It is thought that 

 the effort becomes incorporated into the metaphysical acquisitions 

 of the parent, and is inherited with other metaphysical qualities 

 by the young, which during the period of growth is much more 

 susceptible to modifying influences and is likely to exhibit struct- 

 ural change in consequence. Certain it is that acceleration ceases 

 with growth, and, as the young of animals are not in complete re- 

 lation with the surrounding world, the influences controlling it 

 must be inherited. This consideration renders it doubly probable 

 that the results of effort on the part of the parent appear in change 

 of structure in the offspring. 



Of course, immense numbers of cases of continued effort can be 

 produced by the objector, in which no structural modification has 

 resulted. There are various reasons why a modification should 

 not take place. In the first place, the exertion of use must be 

 great, habitual, and long-continued ; in the next place, abundant 

 food must be at hand ; finally, growth-force must be to spare in 

 the growing young, either from some less necessary part or by ex- 

 cess. Now, cases are probably not rare where none can be spared 

 from another part without injuring the efficiency or viability of 

 the animal ; hence, all such changed individuals would perish 

 through some form of natural selection or disease. 



Domesticated animals can be pointed out where effort and use 

 have long been put forth in the service of man without changing 

 structure. But such effort is not to be compared for a moment 

 with that put forth by animals in a wild state, in seeking food or 

 protection from enemies. The protection furnished by man, and 

 consequent release from the struggle for existence, has reduced 

 tlie chances for such variations greatly. Nevertheless, variations 

 profitable to man have resulted ; witness the race-horse and carter. 



In cases where one side of the body is used in excess of the 

 other, unsymmetrical development would be counteracted by the 

 law of polar or centrifugal growth, all that might be acquired by 

 the one side being inherited by both. Even this original sym- 

 metry has, how^ever, been overcome in some types, as in the 

 flounders (in the jaws and teeth as used parts). This part of 



