The central nervous system of Branchiostoma includes a hollow dorsal neural tube or nerve cord lying mid-dorsally . It has no ganglia. Its anterior end terminates in the rostrum. It has slight enlargement brain called cerebral vesicle. The posterior part called the spinal cord. The narrow canal called neurocoel. It dilates within the cerebral vesicle forming its ventricle.At the roof arise pouch -like blind dorsal diverticulum that extends behind the central canal. The cerebral vesicle contains two receptor organ a pigment spot infundibular organs on its floor. It consists of inner grey matter of nerve cells surroundings the central canal and outer white matter of nerve fibres. These enables the animal to contract suddenely and violently in case of danger.
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