The pineal gland is associated with:

....... plays a very important role in the regulation of a $24$ hours rhythm of our body.

The $24$ hour (diurnal) rhythm of our body,such as the sleep-wake cycle,is regulated by the hormone:

The pineal body originates from:

Identify the correct gland on the basis of the following characteristics:
$(I)$ It is located on the dorsal side of the forebrain.
$(II)$ It plays a very important role in the regulation of the $24$-hour rhythm of our body.
$(III)$ It helps in maintaining body temperature.
$(IV)$ Its hormone influences metabolism as well as defense capability.

Which gland plays a very important role in the regulation of the $24$-hour (diurnal) rhythm of our body?