Unmyelinated axon ( Remak, 1837 ) : An axon (K├Âlliker, 1896) with no myelin sheath. Axons below a threshold diameter characteristic of particular species remain unmyelinated, thus forming the set of thinnest axons; see Williams (1995, pp. 951-954). The (unmyelinated) axon was discovered by Remak (1837) who called it a primitive band.