Life Sciences Term 1

Amniotic Egg

• This is the egg laid by reptiles, birds and some mammals
  
• The embryo develops inside the amnion and is protected by many membranes and hard shell
  
• Amniotic fluid protects the embryo from drying out
  
• It feeds from the yolk
  
• The allantois removes metabolic wastes
  
• The chorion supplies oxygen, food and water
  

Evolutionary advantage

• A critical evolutionary development for terrestrial animals is the reptilian amniotic egg, now also characteristic of birds and some mammals
  
• The developing embryo, protected from drying out, can survive out of water and in a variety of habitats
  
• The yolk provides it with food, and the albumen supplies water and nutrients
  
• Wastes are released to the allantois, an extension of the embryonic gut
  

• Oxygen diffuses easily through the thin outer shell of the egg; its passage to the embryo is regulated by the chorion.