Final answer:
The primary function of the Cowper's glands (bulbourethral glands) is to produce a lubricating and neutralizing fluid for the urethra, not to produce the bulk of seminal fluid or propel sperm from the testicles.
Step-by-step explanation:
The primary function of the Cowper's glands, also known as the bulbourethral glands, is to produce fluid that helps clean and lubricate the urethra. These glands secrete a clear, alkaline fluid rich in proteins shortly before ejaculation, which lubricates the end of the urethra and neutralizes any acidic urine that may be present. This pre-ejaculatory fluid, often referred to as pre-ejaculate, also plays a role in lubricating the vagina. The Cowper's glands are each about the size of a pea and are situated below the prostate gland, with a short duct that carries the secretions into the urethra. Contrary to some beliefs, this fluid can contain sperm and therefore may contribute to the possibility of pregnancy even with the withdrawal method.
It is important to note that the primary function of the bulbourethral glands is not to produce the bulk of the seminal fluid, which is mainly produced by the seminal vesicles and the prostate gland. These glands contribute approximately 60% and 30% to the semen volume, respectively, providing important nutrients and substances that aid in sperm motility and survival in the acidic environment of the female reproductive tract.