Of course, like so many other great men, Wallace was one of those boys whose minds never grow old. Read in his autobiography how on the day he first discovered a new species of butterfly it gave him a violent headache, and he had to go to bed to get rid of it and quiet his nerves--he was that worked up! Darwin was much the same sort of a man. Everything in the world was interesting to him. He wrote a whole book about "Fish Worms," for example. And although probably the most famous man in the history of natural science he was as humble as could be, always looking for the truth and ready to accept criticisms no matter how much they might upset his own previous conclusions, provided these opposing views were supported by evidence. Of course you will want to know more about his life, and you will find more in the "Life and Letters of Charles Darwin," edited by his son. How do you suppose this boy began being a great man--by collecting beetles! Beetles and outdoor sport were his chief delight. USE OF THE INDEX SOME THINGS YOU CAN DO WITH THIS INDEX I shouldn't be surprised if you thought that an index was the dullest part of a book. But it all depends! As a matter of fact, with your help, I am sure I can make this index of ours one of the most interesting things in the whole story; for, like the H. & S., it gives you a chance to "come into the game." The mind enjoys books and grows upon them much as the body grows on food, but, as in the case of both food and books--and books are food--the good you get depends not only on the food but _how you season it and eat it_. You can't expect _everything_ of the cook! Everybody knows, of course, how to use an index to look things up once in a while and it saves time if the index not only tells the page on which a given subject is referred to, but conveys some idea of what that reference is about, as this index tries to do. If, for example, you are studying the Alpine regions in school you may already have covered the question of how flowing water carves mountain valleys, but you may not have had anything about why the Alps don't run north and south, as so many of earth's great ranges do; and so what could be a more interesting thing for you to take into those delightful class discussions? Your teacher knows, although you may not have realized it, that these class talks and debates by the pupils themselves are _the big thing_ in modern teaching. The best education, we know nowadays, isn't the mere cramming down of facts, as people used to think. _It's training in thinking, and in standing on one's own feet!_