Earthworm - Nervous System
The earthworm has a simple yet sensitive nervous system. Its cerebral ganglion, or brain, is connected to the ventral nerve cord, which runs the length of its body. At each segment, segmental ganglion branch off from the ventral nerve cord, thus connecting every segment to the earthworm's brain. Each segmental ganglion must be well coordinated with each other since they must interact in order to control muscle contractions in each segment that are responsible for locomotion. Thanks to this responsive nervous system, an earthworm is sensitive to touch, light from in front or in back, moisture, chemicals, temperature, and vibrations (Loretto).
1) Anus 2) Intestine 3) Cerebral ganglion 4) Prostomium 5) Mouth
6) Nerve collar 7) Segmental ganglion 8) Pharynx 9) Esophagus
10) Segmental nerve 11) Crop 12) Gizzard 13) Ventral nerve cord
Picture retrieved from http://www.student.loretto.org/zoology/phylum_annelida.htm