Why should the vertebrate series have risen through the fish, the reptile, the mammal, to man, unless the manward impulse was inherent in the first vertebrate; something that struggled, that pushed on and up from the more simple to the more complex forms? Why did not unicellular life always remain unicellular? Could not the environment have acted upon it endlessly without causing it to change toward higher and more complex forms, had there not been some indwelling aboriginal tendency toward these forms? How could natural selection, or any other process of selection, work upon species to modify them, if there were not something in species pushing out and on, seeking new ways, new forms, in fact some active principle that is modifiable? Life has risen by stepping-stones of its dead self to higher things. Why has it risen? Why did it not keep on the same level, and go through the cycle of change, as the inorganic does, without attaining to higher forms? Because, it may be replied, it was life, and not mere matter and motion--something that lifts matter and motion to a new plane. Under the influence of the life impulse, the old routine of matter--from compound to compound, from solid to fluid, from fluid to gaseous, from rock to soil, the cycle always ending where it began--is broken into, and cycles of a new order are instituted. From the stable equilibrium which dead matter is always seeking, the same matter in the vital circuit is always seeking the state of unstable equilibrium, or rather is forever passing between the two, and evolving the myriad forms of life in the passage. It is hard to think of the process as the work of the physical and chemical forces of inorganic nature, without supplementing them with a new and different force. The forces of life are constructive forces, and they are operative in a world of destructive or disintegrating forces which oppose them and which they overcome. The physical and chemical forces of dead matter are at war with the forces of life, till life overcomes and uses them. The mechanical forces go on repeating or dividing through the same cycles forever and ever, seeking a stable condition, but the vital force is inventive and creative and constantly breaks the repose that organic nature seeks to impose upon it.