It is therefore of great importance that when a human life begins should be clearly understood. Some Definitions Other attempts have been made to confuse, and new terminologies have been invented and old ones altered. This implies therefore that the embryo does not come into existence until the union of the two pro-nuclei. It is a term of convenience to allow for the experimentation on new life after fertilization and before the union of the two pro-nuclei. It was in the middle of the 19th century that it was established that reproduction of organisms was effected by the phenomenon of cell division.
Nature prepares a long way ahead in reproducing the species.
In the human female, as early as 19 days after conception, a number of cells is selected which will migrate to the developing ovary. When the fetus is 3 months old, they begin a long slow process of maturation during which the number of chromosomes is halved. This process of chromosomal reduction is completed at ovulation with the extrusion of the first polar body when the egg is then ready for fertilization. If it is not united to a sperm cell it will die within 24 hours. The progenitors of the sperm cells are likewise set apart in the 19-day male embryo and eventually take their place in the developing testes.