A zygote (from Greek ζυγωτός zygōtos “joined” or “yoked”, from ζυγοῦν zygoun “to join” or “to yoke”), is cell formed when two gamete cells are joined by means of sexual reproduction. In multicellular organisms, it is the earliest developmental stage of the embryo. In single-celled organisms, the zygote divides to produce offspring, usually through mitosis, the process of cell division. In multicellular organisms, a zygote is always synthesized from the union of two gametes, and constitutes the first stage in a unique organism’s development. Zygotes are usually produced by a fertilization event between two haploid cells—an ovum (female gamete) and a sperm cell (male gamete)—which combine to form the single diploid cell. Such zygotes contain DNA derived from both parents, and this provides all the genetic information necessary to form a new individual. In land plants, the zygote is formed within a chamber called the archegonium. In seedless plants, the archegonium is usually flask-shaped, with a long hollow neck through which the sperm cell enters. As the zygote divides and grows, it does so inside the archegonium. With onset of the first cellular divisions, an animal zygote transforms into a morula, or a mass of cells. Oscar Hertwig and Richard Hertwig made some of the first discoveries on the zygote formation.