156 ACQUIRED CHARACTERS sec. 



specific external stimuli, so closely allied to the stimulus of 

 touch to which they respond, must have gradually produced 

 their specific nature. Only by use, by constant exercise, can 

 they be specifically maintained, and by use, at the same time, 

 they are improved. 



In tliese considerations, the truth of which is undeniable, 

 lies the best proof of the great importance of use, the great 

 importance of acquired and inherited characters, in the modi- 

 fication of orcjans. 



Thus every organism owes its peculiar structure essentially 

 to the use of its parts ; nay more, owes its continued existence 

 exclusively to this exercise and the unceasing action of external 

 stimuli. Without any exercise all our organs would degener- 

 ate ; we should perish as surely as if we were dead, if only for a 

 moment external stimuli ceased their action upon us. Life 

 is truly nothing else than the expression of the interaction 

 between the organism and the stimuli of the external world, 

 and natural oradual death is due to the fact that the oro'anism 

 becomes incapable of receiving stimuli. 



Thus the statement that the eyes of animals living in 

 darkness are atrophied through disuse may be more exactly 

 rendered into this, that the cessation of the stimulus of light 

 causes the pigment to fade, and must therefore cause deteriora- 

 tion of the eyes. 



For the rest, in the preceding it was my intention only to 

 point out that stimulation from without, i.e. use, according 

 to my view, even without selection, must necessarily form 

 organs, strengthen, and perfect them, and I did not think of 

 denying the fact of the influence of selection, c/j. in the 

 formation of eyes. 



Among the examples which Lamarck brings forward in 

 support of the modification of organs by use, and which are, 

 it is true, in most cases, partially to be referred to selection, 

 is one to which I have to devote further consideration. He 



