The embryonic period is the length of time from the beginning of the fragmentation of the zygote to the exit of the body from the egg or germ membranes. The postembryonic stage begins after birth or exit from the egg membranes. In organisms, two types of ontogenesis are distinguished: direct and indirect. The indirect type is characterized by the fact that the egg contains few nutrients necessary to complete development. Therefore, there is a larval stage at which special larval adaptations are formed. For example, the tadpole is characterized by a streamlined body shape, gills, tail, sideline, and other features for living in water. This is a larval type of ontogenesis. A direct type of ontogenesis is characteristic of birds, reptiles, and mammals. The stage of the larva is absent. In birds and reptiles, the eggs are rich in yolk, the embryo develops in dense egg shells, it is well protected and provided with nutrients. In mammals, development occurs in the womb, such a development is called intrauterine.
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.