Unmyelinated axons have because the signal must make its way down the entire length of the axon.

Slower rate of transmission - this is because it cannot carry out saltatory conduction. Myelin insulates nerve cells along the axon and is present as Schwann Cells on the outer membrane. It allows saltatory conduction to take place as the impulse can just from one Schwann Cell to the next without having to travel the whole length of the axon - but this cannot take place in unmyelinated neurones.