Allantois a sac-like structure that grows out of the digestive tract of the embryo. It functions in gas exchange and collects metabolic wastes from the embryo. Surrounds the embryo and cushions it with the fluid it contains. The yolk sac which contains the food for the embryo. They are covered by a thick dry skin covered with scales made of a protein called Keratin .
Reproduction is sexual with internal fertilization.
Most are oviparous , while some snakes and lizards are ovoviviparous. Respiration occurs through well developed lungs, and in some turtles a moist cloacal surface. Reptiles are ectotherms. Most reptiles contain a 3 chambered heart with a partially divided ventricle. Crocodiles contain a 4 chambered heart.