The organ which was considered vestigial until recently but is now confirmed to be an endocrine gland is:

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.

Daily rhythms are usually associated with

Melatonin is secreted by:

Melatonin is secreted by ..........

Which of the following helps in the maintenance of the normal rhythm of the sleep-wake cycle?