1. A pouch or sac in many male invertebrates and lower vertebrates that is used for storing sperm.

2. One of a pair of glands in male mammals that secrete a liquid component (seminal fluid) of semen into the vas deferens. This secretion is alkaline, which neutralizes the acidic conditions in the female genital tract, and contains fructose, used by the sperm as a source of energy. In humans, seminal fluid is thickened by the presence of mucus and the protein fibrinogen; it accounts for 60% of the volume of semen.