BRANCHIOSTOMA-HATSCHEK'S GROOVE

The pit and groove of  Hatschek present in the roof of oral hood are considered sensory organs of unknown function.

BRANCHIOSTOMA-CEPHALIC PIGMENT SPOT

It is large pigmented spot on the anterior wall of cerebral vesicle. It is act as cerebral eye. but it lacks a lens and is also not photosensitive. It is supposed to shield the ocelli from any frontal stimulation by light and probably acts as a thermoreceptor.

BRANCHIOSTOMA-NERVES, OCELLI

The  Peripheral nervous system includes paired nerves from nerve cord.The two pair arising from cephalic vesicle are called cerebral nerves. They lack ventral roots. They are sensory in nature and convey impulses from receptors of snout, oral hood and buccal cirri to the nerve cord.The nerves arising from nerve cord behind the cerebral vesicle are called spinal nerves. Each pair of spinal nerves actually includes separate dorsal and ventral nerve roots .Dorsal nerve root is both sensory and motor and passes out to skin between myotomes. The ventral nerve root is motor and opposite to the myotome .The dorsal and ventral roots of a pair do not originate at the same level and the dorsal root of one side lies opposite the ventral root. The dorsal root is single the ventral root is made of several branches. Nerves of amphioxusare primitive and non-myelinated is not covered by a sheath of myelin in the vertebrates.
OCELLI-These are photoreceptors or light-sensitive organs on the ventro-lateral sides of nerve cord. They are originated in different directions and help the animal in burrowing in sand or in swimming spirally to perceive light from all directions. The eye spot or ocelli is made up of two cells an outer pigment cell or melanocyte and inner photosensitive cell with a striated apicalborder which serves as a lens. The photosensitive cell sends a fine nerve fibre to the nerve cord.

BRANCHIOSTOMA-NERVE CORD

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.

BRANCHIOSTOMA-AUTONOMIC NERVOUS SYSTEM

It consist of two nerve plexes in the gut wall connected to nerve cord plexes in the gut wall connected to nerve cord by visceral .The autonomous system control the involuntary muscles of the gut wall. Sympathetic ganglia are lacking.

BRANCHIOSTOMA-NERVOUS SYSTEM

The nervous system is very simple. The well developed brain, as found in higher chordates is absent.

BRANCHIOSTOMA-BROWN FUNNELS

The two sac like brown funnel are situateddorsally upon the posteroor end of pharynx. The narrow anterior end of each funnel opens into the epibranchial or dorsal coelomic canal of its side.. Most the funnel where the excretory while of to be receptor organs.