The posterior lobe of pituitary gland is not a 'true' endocrine gland because: It is under the regulation of hypothalamus. It secretes enzymes. It is provided with a duct. It only stores and releases hormones.

Oxytocin and vasopressin hormones are produced by the hypothalamus but stored and are released into the bloodstream via the posterior pituitary. That's the reason why it is not a true endocrine gland. Endocrine glands are the ductless glands that secrete and release hormones in the blood directly.Therefore, the correct answer is option D.