Ganglia and nucleus : similarity and difference

Nucleus : 

collection of nerve cells bodies within the central nervous system.

SN:

1. Big collection of nerve cells body within the central nervous system is known as grey matter. 
2. Small collection of nerve cells body within the central nervous system is known as nucleus. 
3. Some time part of grey matter is also known as nucleus. 
4. Some time the axons of nucleus leaves the central nervous system as peripheral nerve

Ganglia : 

Collection of nerve cells bodies outside the central nervous system is known as ganglia.

SN:

Nerve cells bodies of ganglia some time synapses with axon of other neuron 

Some time axon of other neuron only passage through the ganglia 

Some time ganglia connect with each other so axon of one ganglia passage above ganglia or below ganglia 

Some ganglia near to central nervous system but some are nearer to target organ 

Similarity between nucleus and ganglia : both are collection of nerve cells bodies 

Difference between nucleus and ganglia: nucleus lies within CNS and ganglia lies within PNS