It takes between 10 and 20 years for a tuatara to reach sexual maturity. The female, on average, lays between 5 and 18 eggs only once every 4 years, the longest reproductive cycle of any reptile. Mating occurs from mid-summer to early autumn (January-March) and the eggs are laid the following spring or early summer (October-December). Incubation takes from 12 to 15 months, with the development of the embryo stopping during the winter months. Thus, a hatchling tuatara would have been conceived over two years earlier. The male is devoid of any external sex organs, and copulation is achieved by a meeting of the cloacal regions in what is known as a "cloacal kiss."