Semen is the fluid that is discharged by the male reproductive organs. It is composed of sperms and viscous fluid to facilitate the flow of sperms to the female genital tract. It consists of fluids secreted from various glands. The seminal vesicles secrete about 70% of the semen. It consists of fructose. The prostrate gland secrete about 20% volume of the semen. The fluid consists of acid phosphatase, and proteolytic enzymes. The bulbourethral gland secretes about 5% of the total volume of semen. It consists of mucoproteins.
The clotting factors or enzymes are absent in semen as these are produced by the blood platelets at the site of injury.
Certain fossils, called index fossils, help geologists match rock layers. To be useful as an index fossil, a fossil must be widely distributed and represent a type of organism that existed for a brief time period.
