The basic function of the reproductive system of all sexual organism is to accomplish fertilization. Fertilization is the union of the nuclei of two appropriate gametes with one another. In most higher animals fertilization is atteined by the fusion of the nucleus of the egg cell with that of the sperm. In virtually all mammals including man the reproductive system has the added role of insuring the successful development of the embryo into a new individual within the body of the female. The reproductive system in vertebrates is the only system of the body that exists in two morphologically and functionally different states thus accounting for two different types of individuals, male and female. It is essentially composed of the gonads or sex glands (which produce sex cells or gamets) and the ducts or passageways which permit the transfer of the gametes. An additional primary sexual structure, the copulatory organ or penis, has evolved in the males of some animals, such as the mammals, permitting the deposition of sperm within the ducts of the female reproductive system (Nason, 1965).
The reproductive system of the human female consists primarily of two ovaries (or the female gonads) which produce the female gametes or egg cells, and associated ductd and structures. The latter include the fallopian tubes ar oviduct, uterus, vagina, and vulva. Each of the two adult ovaries is about the size and shape of a large almond region of the abdominal cavity. The surface of the ovary consists of a layer of columnar epithelial cells which at various intervals penetrate deeply as columns of cells into the underlying connective tissue (Nason, 1965).
The male reproductive system in human consists of two primary sex glands, the testes, which produce the sperm, and a series of ducts, accessory glands, and supporting structures. Each of the two testes in the adult male is an avoid body about the size of a walnut. Both are located outside the body cavity within a skin-covered pouch called the scrotum or the scrotal sac. In other vertebrate such as fish, frog, reptile, and bird, the testes are located within the abdominal cavity. The slightly lower temperature of the scrotum (about 3 to 5 degrees celcius less) compared to the abdominal cavity is believed to be essential for the formation of sperm. (Nason, 1965)
Another vertebrate such as frog also have reproductive system. Reproductive system serves to maintain the frog as a species. It consists of the reproductive organs or gonads, which produce sex cells, and the reproductive ducts through which these cells leave the body. Frogs are of two sexes, the female which lay eggs or ova (singel: ovum), and the males which produce sperm or spermatozoa to fertilize the eggs and cause them to develop into new individuals. Each individual frog is either female or male, the sexes being separate. The female two gonads, or ovaries, are attached dordally in the coelom, near the kidneys, each supported by a mesentry (mesovarium). The ovary is supplied with arteries that bring materials for growth of the ova. Along either side of the middorsal line of the coelom is a whitish convoluted oviduct, its anterior end is an open ciliated funnel (ostium and its posterior and joins dorsally to the cloaca). The male has two small bean-shaped testes attached near the kidneys attached near the kidneys by mesentries . Each testis is a mass of coiled seminiferous tubules where spermatozoa are produced. The minute sperm, when mature, enter several fine ducts, or vasa efferentia, that connect to uriniferous tubules in the anterior part of the kidney. The sperm then pass down the tubules and ureter (which are joint urogenital canals), and may be stored in the dilated posterior end or seminal vesicle, of the ureter (Storer, 1957).
Source: Nason, alvin. 1965. "Text Book of Modern Biology." New York: John Wiley and Sons, Inc.