of creatures which dwell in darkness. There are all stages between total blindness and weak eyes. Now, do these blind creatures live in darkness because they are blind, or have they become first weak-eyed and then blind because of the continuous disuse of their eyes? The former explanation has actually been suggested! Individuals not smitten, but spontaneously, as a freak, born with sore eyes, have crept into the darkness for relief and have produced a blind race! To carry such a notion to the bitter end leads to absurdities. Anyhow, it is not understandable where the benefit of losing the eyesight arises. It can be explained only by continued disuse: witness Spalax typhlus, the blind mole, and, above all, the Endoparasites.
Let us now take an example to explain the influence of a tangible external stimulus. Repeated pressure produces callosities, Although they are not exactly beneficial in the shape of corns on our toes, they are
