How does the embryonic period of development begin and end?

The embryonic period (embryogenesis) begins at the time of the formation of the zygote and ends with birth (for example, in mammals) or exit from the egg membranes (for example, in birds).

Remember: The process of learning a person lasts a lifetime. The value of the same knowledge for different people may be different, it is determined by their individual characteristics and needs. Therefore, knowledge is always needed at any age and position.