THE ADAPTATION OF ORGANISMS 65 



CHAPTER XII 



THE ADAPTATION OF ORGANISMS TO THEIR 

 ENVIRONMENT 



EVERY living organism has a definite relation to the 

 world in which it lives, and in this chapter we must 

 consider how the organisms make the most of their sur- 

 roundings, using such features as are favourable, and 

 protecting them from such as are dangerous either to 

 themselves or their offspring ; in other words, how the 

 organism adapts itself to its surroundings. 



It is fairly manifest that the plant, especially the 

 higher forms, will show more adaptability than the 

 animal, simply because the majority of plants " can't 

 run away." They must therefore adapt themselves 

 either temporarily or permanently to their surroundings 

 or they must cease to exist. 



What are the principal external influences that affect 

 a living organism ? They are mainly mechanical, 

 chemical, physical, and vital. 



Under the first of these, which we have termed 

 mechanical influences, may be placed amount of space, 

 pressure and tension ; then under chemical influences 

 we have such influences as food, air, water, and the 

 medium in which the organism lives ; thirdly, heat, 

 light, electricity, &c. may be grouped together as phy- 

 sical ; and lastly there are the vital influences, the 



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