When the history of the Nineteenth Century--'the Wonderful Century, ' as it has, not inaptly, been called--comes to be written, a foremost place must be assigned to that great movement by which evolution has become the dominant factor in scientific progress, while its influence has been felt in every sphere of human speculation and effort. At the beginning of the Century, the few who ventured to entertain evolutionary ideas were regarded by their scientific contemporaries, as wild visionaries or harmless 'cranks'--by the world at large, as ignorant 'quacks' or 'designing atheists.