Egg membranesEgg membranes

There are 3 types of egg membranes:

1. Primary egg membrane:Formed by the egg itself inside the ovary ; eg. Zona pellucida in mammals and chorion in insects.

2. Secondary egg membrane: Formed by the ovarian tissue before the egg leave the ovary.

3. Tertiary egg membrane: Formed during passage of the egg in the oviduct ; eg. Egg of toad and egg of bird.

FertilizationFertilization

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.