The correct answer is option 4: Pituitary. Lactogenic hormone, also known as prolactin, is secreted by the pituitary gland. The pituitary gland is a small pea-sized gland located at the base of the brain. It is often referred to as the "master gland" because it produces and releases hormones that regulate various bodily functions. One of the hormones produced by the pituitary gland is lactogenic hormone, which plays a crucial role in milk production in mammals. It stimulates the mammary glands in the breasts to produce milk. While the other options mentioned (mammary glands, placenta, and ovary) are indeed involved in the process of lactation, they do not secrete the lactogenic hormone itself.