A bachelor of laws in Michigan writes me in a rather peremptory manner, demanding an answer by return mail as to why robins are evenly distributed over the country instead of collected in large numbers in one locality; and if they breed in the South; and he insists that my answer be explicit, and not the mere statement "that it is natural law." I wonder that he did not put a special-delivery stamp on his letter. He is probably wondering why I am so dilatory in answering. There seems to be an inherent tendency in nearly all living things to scatter, to seek new fields. They are obeying the first command--to increase and multiply. Then it is also a question of food, which is limited in every locality. Robins do not breed in flocks, but in pairs. Every gas is a vacuum to every other gas; and every locality is a vacuum to the different species of birds that breed there. The seed-eaters, the fruit-eaters, the insect-eaters, and the omnivorous feeders, like the robin--in other words, the sparrows, the flycatchers, the warblers--may and do all live together in harmony in the same narrow area. The struggle of which we have heard so much since Darwin's time is mainly a natural sifting and distributing process, such as that going on all about us by the winds and the waters. The seeds carried by the winds do not thrive unless they chance to fall on suitable ground. All may be "fit" to survive and yet fail unless they are also lucky. What so frail as a spider's web, and yet how the spiders thrive! Nature gives the weak many advantages. There is a slow, bloodless struggle of one species with another--the fleet with the slow, the cunning with the stupid, the sharp-eyed and sharp-eared with the dull of eye and ear, the keen of scent with the blunt of scent--which we call natural competition; but the slow, the stupid, the dull-eyed, dull-eared, and dull-scented find their place and thrive for all that. They are dull and slow because they do not need to be otherwise; the conditions of their lives do not require speed and sharpness. The porcupine has its barbed quills, the skunk its pungent secretion. All parts of nature dovetail together. The deer and the antelope kind have speed and sharp senses because their enemies have speed and sharp senses. The small birds are keen-eyed and watchful because the hawks are so, too. The red squirrel dominates the gray squirrel, which is above him in size and strength, and the chipmunk below him, but he does not exterminate either. The chipmunk burrows in the ground where the red cannot follow him, and he lays up a store of nuts and seeds which the red does not. The weasel easily dominates the rat, but the rat prospers in spite of cats and traps and weasels. The sifting of species is done largely by environment, the wet, the cold, the heat--the fittest, or those best adapted to their environment, survive. For some obscure reason they have a fuller measure of life than those who fall by the way. III. HEADS AND TAILS