Reproduction

Although a wide range of reproductive modes are used by snakes; all snakes employ internal fertilization, accomplished by means of paired, forked hemipenes, which are stored inverted in the male's tail. The hemipenes are often grooved, hooked, or spined in order to grip the walls of the female's cloaca.
Most species of snake lay eggs, and most of those species abandon them shortly after laying; however, individual species such as the King cobra actually construct nests and stay in the vicinity of the hatchlings after incubation.Most pythons coil around their egg-clutches after they have laid them and remain with the eggs until they hatch. The female python will not leave the eggs, except to occasionally bask in the sun or drink water and will generate heat to incubate the eggs by shivering.
Some species of snake are ovoviviparous and retain the eggs within their bodies until they are almost ready to hatch. Recently, it has been confirmed that several species of snake are fully viviparous, such as the boa constrictor and green anaconda, nourishing their young through a placenta as well as a yolk sac, which is highly unusual among reptiles, or anything else outside of placental mammals. Retention of eggs and live birth are most often associated with colder environments, as the retention of the young within the female.