1. Egg membranes There are 3 types of egg membranes:
Primary egg membrane:Formed by the egg itself inside the ovary ; eg. Zona pellucida in mammals and chorion in insects.
Secondary egg membrane: Formed by the ovarian tissue before the egg leave the ovary.
Tertiary egg membrane: Formed during passage of the egg in the oviduct ; eg. Egg of toad and egg of bird.

2. Fertilization
Fertilization occurs either external in aquatic animals or internal terrestrial animals .
Steps of fertilization:
1. Ovulation.
2. Egg transport.
3. Sperm transport.
4. Penetration of the egg.
5. Fusion between egg & sperm.
6. Prevention of polyspermy.
7. Decondensation of egg and sperm nucleus.
8. Metabolic activation of the egg.