General characteristics

• These are true terrestrial animals and need not return to water to reproduce. The female’s oviduct secretes a protective leathery shell around the egg, which helps to prevent the developing embryo from drying out. Since sperm cannot penetrate this shell fertilization must occur within the body of the female (internal) before the shell is added.
• Most have three-chambered heart, but crocodiles have four chambers.
• Their body is divided into head, neck, trunk and tail.
• They are cold-blooded or poikilothermic; have limbs with 5 clawed digits. Example Crocodiles, alligators, turtles, lizards

External and internal features of a lizard

External features of a lizard

Dry skin: with scales enables them to survive in dry environment.
Nostril: sense smell
Ear drum: conducts sound wave for hearing
Limbs: with five digits and claws
Tail: wriggles during their motion
Cloaca: to discharge gametes and waste

Internal structures

Tongue: with sticky tip to catch their insect meal.
Teeth: inserted in jaws to seize and capture prey
Kidney: to make and remove urine
Lung: for breathing
Ovaries: for production of shelled egg after fertilization

Internal fertilization and the amniotic egg

The eggs of reptiles are fertilized internally before they are deposited. The male reptiles utilize a tubular organ, the penis, to inject sperm into the female. Most reptiles are oviparous, laying eggs and then abandoning them. These eggs are surrounded by a leathery shell that is deposited as the egg passes through the oviduct. Other species of reptiles are ovoviviparous or viviparous, forming eggs that develop into embryos within the body of the mother.