56 THE FOUNDATIONS OF ZOOLOGY 



making any essential change. One morning, some time ago, I 

 •found in my mail two papers by naturalists whose well-earned 

 reputation in their own fields would seem to entitle them to 

 speak with authority. In one I read that American indifference 

 to the destruction of our valuable timber is the inherited effect 

 of the long war with the primeval forest which our ancestors 

 were forced to carry on in order to make a home in the new 

 world. The author of the second paper accounts for the great size 

 of the eyes of certain deep-sea fishes by attributing their enlarge- 

 ment to the efforts of many generations to see in " total " darkness. 



Conrad Gesner tells us, in his " Book of Animals," that no book 

 is so bad the thoughtful reader may not learn something from 

 it ; and if these speculations can be made to point a moral, they 

 are not quite in vain, as they may help us to fix attention on 

 certain first principles which seem so obvious that one would 

 think all must admit them. 



Familiar experience teaches that living things are often greatly 

 modified by the conditions to which they are exposed during 

 their individual life, and that the modifications which are thus 

 produced are often useful ; for if this were not the case, no bene- 

 ficial effect could come from training or education. We all know 

 that the congenital or natural powers and faculties of children and 

 of those who grow up in ignorance are very limited, and that it 

 is practice which makes perfect. That judicious use often devel- 

 ops and strengthens the parts which are used is unquestionable 

 and the efficiency of neglected organs often becomes impaired. We 

 are born with a nature that makes the normal use of our powers 

 a pleasure, and while aceticism may despise mere bodily delights, 

 more generous wisdom sees, in the keen enjoyment of normal or- 

 ganic life, and in the discomfort or pain which attends repression, 

 especially in the young, some of those wonderful adjustments 

 which are the very essence of natural science. 



While hard work is exhausting, and while the organic machine 

 is easily damaged by abuse, and is, at last, worn out by use, normal 

 use is a condition of its perfect development, and the amount of 

 normal work it may do without deterioration is astonishing. In 

 the highly civilized and self-indulgent, it is much less likely to 

 wear out than to rust out; and nothing could be more short- 



