78 FOOT-NOTES TO EVOLUTION. 



were no break in the uniformity of the environment, 

 there would be no need of such knowledge. If there 

 were no variation in lights and shadows, the eye would 

 be powerless to bring information. The senses deal 

 with changes or breaks in reality rather than with reali- 

 ties themselves. Because, in action, the organism must 

 be obedient to the demands of its environment, it is the 

 function of the eye to make known these demands. 

 The existence of the eye is therefore a concession to the 

 environment. A concession of like nature is the brain 

 itself, of which the eye and the sense organs in general 

 may be considered as prolongations. These appendages 

 of the brain carry to it truth of varying kind or degree. 

 This truth as to external nature furnishes the basis of 

 that obedience which in the animal expresses itself in 

 action. 



The respiratory apparatus is an adaptation for the 

 purpose of purifying the blood from the waste produced 

 in the processes of life. It is a concession on the one 

 hand to the demands of life in cell and tissue, and on 

 the other hand to the nature of the surrounding medium. 

 A change in the atmosphere would demand a correspond- 

 ing change in the organs of breathing. If such a con- 

 cession were impossible, the species in question would 

 become extinct, as its individuals would perish. If the 

 concessions necessary to continued existence should in- 

 volve changes in other organs, the process of the sur- 

 vival of the obedient would in time produce these 

 changes. 



If there were no surrounding medium there would be 

 no organ of respiration. If there were no light there 

 would be no organ of vision. If there were no sound 

 there would be no ear. If there were no motion there 

 would be no need for knowledge, and therefore no sen- 

 sation. If there were no power of locomotion there 



