1. Planaria is a flatworm and belongs to the phylum Platyhelminthes.
2. It is the most primitive animal with a Central Nervous System (CNS) located on the ventral side of body.
3. Nervous system consists of a mass of cerebral or cephalic ganglion appearing like an inverted U shaped brain.
4. Ventrally from below the ganglia arise a pair of Ventral Nerve Cords (VNC) or long nerve cords. These are interconnected to each other by transfer nerve or commissure in a ladder like manner.
5. The PNS include sensory cells arranged in lateral cords in the body.
