a mental microscope, be found to contain a residuary element of _its_ opposite, and this again of _its_ opposite, and so on _ad infinitum_, as with mirrors standing face to face. This having been explained, and it being understood that when we speak of design in organism we do so with a mental reserve of _exceptis excipiendis_, there should be no hesitation in holding the various modifications of plants and animals to be in such preponderating measure due to function, that design, which underlies function, is the fittest idea with which to connect them in our minds. We will now proceed to inquire how Mr. Darwin came to substitute, or try to substitute, the survival of the luckiest fittest, for the survival of the most cunning fittest, as held by Erasmus Darwin and Lamarck; or more briefly how he came to substitute luck for cunning. Chapter XII Why Darwin’s Variations were Accidental SOME may perhaps deny that Mr. Darwin did this, and say he laid so much stress on use and disuse as virtually to make function his main factor of evolution. If, indeed, we confine ourselves to isolated passages, we shall find little difficulty in making out a strong case to this effect. Certainly most people believe this to be Mr. Darwin’s doctrine, and considering how long and fully he had the ear of the public, it is not likely they would think thus if Mr. Darwin had willed otherwise, nor could he have induced them to think as they do if he had not said a good deal that was capable of the construction so commonly put upon it; but it is hardly necessary, when addressing biologists, to insist on the fact that Mr. Darwin’s distinctive doctrine is the denial of the comparative importance of function, or use and disuse, as a purveyor of variations,—with some, but not very considerable, exceptions, chiefly in the cases of domesticated animals.