Final answer:
The lung (c) is not a gland in the endocrine system. The pineal, hypothalamus, and ovary are all parts of the endocrine system with various hormonal functions, unlike the lungs, which are part of the respiratory system.
Step-by-step explanation:
The gland in the endocrine system that is not a gland is the lung (c). The pineal gland (a) is known to secrete melatonin, which regulates sleep-wake cycles. The hypothalamus (b), although part of the brain, secretes hormones that control the pituitary gland and is therefore considered part of the endocrine system. The ovary (d) is an endocrine gland that produces hormones such as estrogen and progesterone. The lungs, on the other hand, are primarily organs of the respiratory system and do not serve the same hormonal functions as the endocrine glands. Other endocrine glands include the thyroid, parathyroid, adrenal glands, pancreas, and in some cases, the thymus and reproductive glands like the testes in males.