What is neurilemma ... explain citing its difference with Myelin Sheath

Neurilemma (also known as neurolemma, sheath of Schwann, or Schwann's sheath) is the outermost nucleated cytoplasmic layer of Schwann cells (also called neurilemmocytes) that surrounds the axon of the neuron ... In the central nervous system, axons are myelinated by oligodendrocytes, thus lack neurilemma.