The correct answer is option 4, Spleen.

Option 1, Pituitary - The Pituitary gland is an endocrine gland located at the base of the brain. It produces and secretes hormones that regulate various body functions.

Option 2, Thyroid - The Thyroid gland is also an endocrine gland located in the neck. It produces hormones that regulate metabolism and growth.

Option 3, Adrenal - The Adrenal glands, located on top of the kidneys, are endocrine glands that produce hormones such as adrenaline and corticosteroids that help regulate metabolism and respond to stress.

Option 4, Spleen - The Spleen is not an endocrine gland. It is an organ in the lymphatic system responsible for filtering blood and producing immune cells, but it does not produce hormones.

Therefore, the correct answer is option 4, Spleen.