The reproductive system is a group of plant or animal organs which are necessary for the production of offspring. The major structures which are involved in reproduction are known as the gonads. The basic units of sexual reproduction are the male and female germ cells.

Germ cells are those cells which do not differentiate when an embryo is developing. Cells which develop into tissues and organs are called somatic cells. In invertebrates, the germ cells congregate in the body cavity or the circulatory system, while in vertebrates, they move to tissues which eventually become the gonads, or reproductive organs. When an organism reaches sexual maturity, the germ cells undergo numerous cell divisions and eventually develop, through a process called meiosis, into the mature reproductive cells, the gametes. Gametes contain half the number of chromosomes of the somatic cells.

Male and female gametes are produced and stored...