Egg-laying is the ancestral trait for reproduction of lizards. Their eggs are similar in structure to those of birds. Lizard eggs have calcified eggshells that protect the egg sac, while inside is a yolk that nourishes the embryo (Figure 1). The eggs are laid while the embryo is immature and undeveloped, and they are then incubated externally in a nest where the embryo develops to the point where it hatches and emerges as a free-living juvenile lizard.
Live birth differs from egg-laying because no eggshells are involved. The embryos are incubated inside the mother until they are fully developed to the point of being free living, and then they are born. In some lizards there is parental care of the young, but in most cases the young are completely independent from birth.
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