"The ancient and medieval theory can be called an "organismic" theory: it treated the motion of inanimate bodies (such as rocks) by analogy with the motions of animals. Just as... a dog... performs a certain motion... to obtain... meat, medieval mechanics assumed that a stone fell in order to reach its "natural place." ...Beyond the ring of fire... began the realm of celestial bodies or of [seven] planetary spheres, regarded as rotating. These celestial bodies consisted of a much more subtle matter than terrestrial bodies. To each... belonged a spirit, a kind of god. ...they consisted of a nonterrestrial material. ...described by some authors as crystalline spheres. ...they moved in a most perfect way—in permanent, uniform, circular motion. ...The eighth sphere [was] of the fixed stars... supposed to be fixed on... it. Beyond the eighth sphere was heaven. ...Eventually the idea of a "prime mover" or "" developed—that beyond the eighth sphere was a ninth which did not move itself, but which moved everything."