The agile lizard and the scaly order

Reptiles are the first truly land animals: the skin is dry and takes no part in breathing, they breathe only with lungs, and they lay eggs on land. The agile lizard lives in deserts and foothills, eats insects and is 15–20 cm long with its tail. Its grey-green colour hides it from predators in grass. The head is movable, and the eye has an upper lid, a lower lid and a blinking third lid that keeps the eye moist. The eardrum behind the eye covers the outer ear opening, and the forked tongue is an organ of touch and taste. The legs grow from the sides of the body, so the belly drags on the ground. Horny scales cover the dry skin and limit growth, so the lizard grows by moulting several times in summer and shedding its old skin. Inside, a rib cage (chest vertebrae, ribs, breastbone) has appeared; the lungs are more complex than a frog’s, with walls divided into small chambers, which gives a larger gas-exchange surface. The heart is three-chambered but more complex than a frog’s; body temperature depends on the surroundings (cold-blooded), and in cold the animal becomes torpid. The cerebellum is well developed, so movement is agile. Fertilisation is internal; 5–15 large, yolk-rich, thick-shelled eggs are buried shallowly in a sunny spot. A small lizard that looks like the adult hatches, with no larval stage. If a predator grabs the tail, the lizard drops part of it and escapes, and the tail later regrows – this is regeneration.