Period Of the Zygote(fertilization to end of second week))
- The size of the zygote-that of a pinhead remains unchanged because it has no outside source of nourishment, it is kept alive by yolk in the Ovum
As The zygote passes down the fallopian tube to uterus, it divides many time separates into an outer and an inner layer.
The outer layer later develops into the placenta,the umbilical cord,and the amniotic sac,and the inner layer develops into a new human being.
About ten days after fertilization, the zygote becomes implanted in the nuterine wall.