Ganglia - Organisation of Nervous System
In between higher non-chordates with a central nervous system, you will observe that the association neurons and motor neurons are concentrated in masses called ganglia, and the bipolar, sensory neurons are distributed peripherally in association along with sense organs. Invertebrate ganglia contain a cellular rind or cortex and a central mass called neuropile.
Figure: Cross sections through (A) abdominal ganglion and (B) inter-ganglionic connective to show general structure.
The neuropile is made up of nerve fiber mass, criss crossing in all directions Axons of sensory neurons terminate in the neuropile and those of motor neurons arise from it.