For years Descartes's idea of the function of this gland was held by many physiologists, and it was only the introduction of modern high-power microscopy that reduced this also to a mere mechanism, and showed that it is apparently the remains of a Cyclopean eye once common to man's remote ancestors.
Descartes was the originator of a theory of the movements of the universe by a mechanical process--the Cartesian theory of vortices--which for several decades after its promulgation reigned supreme in science.

It is the ingenuity of this theory, not the truth of its assertions, that still excites admiration, for it has long since been supplanted.

It was certainly the best hitherto advanced--the best "that the observations of the age admitted," according to D'Alembert.
According to this theory the infinite universe is full of matter, there being no such thing as a vacuum.

Matter, as Descartes believed, is uniform in character throughout the entire universe, and since motion cannot take place in any part of a space completely filled, without simultaneous movement in all other parts, there are constant more or less circular movements, vortices, or whirlpools of particles, varying, of course, in size and velocity.

As a result of this circular movement the particles of matter tend to become globular from contact with one another.