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Page:Popular Science Monthly Volume 18.djvu/109

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there is some excuse for the over-abundance of creatures which life thrusts into the world.

But there is something deeper than this to consider. If in a large school every boy had a prize at the end of the half year, whether he had worked or not, do you think all the boys would work as hard as they do or learn as well? If every man had all he required and could live comfortably, and bring up his children to enjoy life without working for it, do you think people would take such trouble to learn trades and professions, and to improve themselves so as to be more able than others? Would they work hard day and night to make new inventions, or discover new lands, and found fresh colonies, or be in any way so useful or learn so much as they do now?

No, it is the struggle for life and the necessity for work which make people invent and plan, and improve themselves and things around them. And so it is also with plants and animals: life has to educate all her children, and she does it by giving the prize of success, of health, and strength, and enjoyment to those who can best fight the battle of existence, and do their work best in the world.

Every plant and every animal which is born upon the earth has to get its own food and earn its own livelihood, and to protect itself from the attacks of others. Would the spider toil so industriously to spin her web if food came to her without any exertion on her part? Would the caddis-worm have learned to build a tube of sand and shells to protect its soft body, or the oyster to take lime from the sea-water to form a strong shell for its home, if they had no enemies to struggle against and needed no protection? Would the bird have learned to build her nest or the beaver his house if there were no need for their industry?

But as it is, since the whole world is teeming with life, and countless numbers of seeds and eggs and young beginnings of creatures are only waiting for the chance to fill any vacant nook or corner, every living thing must learn to do its best and to find the place where it is most useful, and least likely to be destroyed by others. And so it comes to pass that the whole planet is used to the best advantage, and life teaches her children to get all the good out of it that they can.

If the ocean and the rivers be full, then some must learn to live on the land, and so we have, for example, water-snails and land-snails, and whereas the one kind can only breathe by gills in the water, the other breathes by means of lungs in the air, while between these are some, such as the river-snails of the tropics, which have both gills and lungs, and can breathe in both water and air. We have large whales sailing as monarchs of the oceans, and walruses and seals fishing in its depths for their food, while all other animals of their kind live on the land.

Then, again, while many creatures love the bright light, others take advantage of the dark corners where room is left for them to live. You can not lift a stone by the seaside but what you will find some living thing under it, nor turn up a spadeful of earth without disturb-