THE SIZE OF LIVING THINGS thousand million. Echinodcrms have only a range of a million times, rotifers even less. As proof of how soon the size of insects and of flying birds is cut short, we find they have ranges of only a million and ten thousand, respectively. Man is a very large organism. During his individual existence he multiplies his original weight a thousand million, and comes to con- tain about a hundred million million cells. He is a little more than halfway up the size-scale of mammals, and nearly two-thirds up that of the vertebrates. Then we look at the range of life as a whole, and compare it with the size-ranges of not-living objects above and below the limits of living things; here too there arc surprises. The sun is almost pre- cisely as much heavier than a big tree as the big tree is heavier than the filter-passer; but the range from the filter-passer downward to the ultimate and smallest unit of world-stuff, the electron, is only half this—only as much as from the big tree to such an easily visible creature as the flea. It takes more tubercle bacilli to weigh one man than there are electrons in a tubercle bacillus. It is possible to calculate, on the Einstein hypothesis, a minimum weight for the whole universe, a minimum figure for the totality of matter. This is nearly io24 times as much as the sun—in other words, the sun is halfway between the big tree and the whole universe of size. Although the molecules of living matter are, for molecules, enor- mous, yet the smallest living organisms are far down on the world's size-scale. Once started, however, life has achieved a size-range which is two-fifths of that from electron to star, and probably well pver a quarter of the whole range of size within the universe. Man is almost halfway between atom and star; he is nearly two-fifths up the cosmic scale from electron to the all-embracing weight of the universe. But so vast is that scale that to be halfway up he would have to be as big as a million big trees rolled into one. Even if we were to take the thousand million people who now inhabit the globe as constituting but one single organism, this would still be more than ten times too small. The individual man is all but halfway between atom and star; humanity entire stands in the same position between electron and universe.