Experimenting and experimenting endlessly, taking a forward step only when compelled by necessity,--this is the way of Nature,--experimenting with eyes, with ears, with teeth, with limbs, with feet, with toes, with wings, with bladders and lungs, with scales and armors, hitting upon the backbone only after long trials with other forms, hitting upon the movable eye only after long ages of other eyes, hitting on the mammal only after long ages of egg-laying vertebrates, hitting on the placenta only recently,--experimenting all around the circle, discarding and inventing, taking ages to perfect the nervous system, ages and ages to develop the centralized ganglia, the brain. First life was like a rabble, a mob, without thought or head, then slowly organization went on, as it were, from family to clan, from clan to tribe, from tribe to nation, or centralized government--the brain of man--all parts duly subordinated and directed,--millions of cells organized and working on different functions to one grand end,--cooperation, fraternization, division of labor, altruism, etc. The cell was the first invention; it is the unit of life,--a speck of protoplasm with a nucleus. To educate this cell till it could combine with its fellows and form the higher animals seems to have been the aim of the creative energy. First the cell, then combinations of cells, then combinations of combinations, then more and more complex combinations till the body of man is reached, where endless confraternities of cells, all with different functions, working to build and sustain different organs,--brain, heart, liver, muscles, nerves,--yet all working together for one grand end--the body and mind of man. In their last analysis, all made up of the same cells--their combinations and organization making the different forms. Evolution touches all forms but tarries with few. Many are called but few are chosen--chosen to lead the man-impulse upward. Myriads of forms are left behind, like driftwood caught in the eddies of a current. The clam has always remained a clam, the oyster remained an oyster. The cockroach is about the same creature to-day that it was untold aeons ago; so is the shark, and so are many other forms of marine life. Often where old species have gone out and new come in, no progress has been made. Evolution concentrates along certain lines. The biological tree behaves like another tree, branches die and drop off (species become extinct), others mature and remain, while some central shoot pushes upward. Many of the huge reptilian and mammalian branches perished in comparatively late times.