One of Penrose's devices for illustrating self-reproduction.

The center element in (fig a) acts like a crystal 'seed' to which the components on its left (fig b) and right (fig c) may bind. When these two elements have bound to the seed, mechanical switches are opened, causing the four-element machine to split down the middle... forming twin two-element machines exactly like the first.

Image posted on this website for your education without the permission of Scientific American. Movies of these devices are available online: Part I, Part II.