Which of these is an accessory reproductive gland in male mammals

The correct option is Prostate gland.

To understand why this is the correct answer, let's break down the role of accessory reproductive glands in male mammals:
Male mammals possess accessory reproductive glands that secrete fluids to constitute the seminal plasma. This seminal plasma, along with sperm, forms semen. The main accessory reproductive glands in male mammals are:
1. Seminal vesicles: Pair of glands that secrete a significant portion of the fluid that becomes semen, rich in fructose and other nutrients.
2. Prostate gland: A single, large gland located just below the urinary bladder. It secretes a slightly alkaline, milky fluid that helps nourish sperm and neutralize the acidity of the vaginal tract, enhancing sperm motility and survival.
3. Bulbourethral glands (Cowper's glands): Secretes a lubricating mucus that neutralizes acidic urine residue in the urethra.

Let's evaluate the given options:
- Inguinal gland: These are scent glands found in the inguinal region (groin) of certain mammals (like rabbits), but they are not part of the male reproductive system.
- Prostate gland: As described above, this is a major accessory reproductive gland in male mammals.
- Mushroom-shaped gland: This is an accessory reproductive gland found in male insects (cockroaches), not mammals.
- Gastric gland: These glands are located in the stomach lining and secrete gastric juice (containing hydrochloric acid and pepsinogen) for digestion, completely unrelated to reproduction.

Therefore, the prostate gland is the correct male accessory reproductive gland in mammals among the choices provided.