When you become a Buddha, there is no more existence, that is, nirvana. The others are the so-called wombbirth, egg-birth, moisture-birth, and transformation-birth, which refer to the four life forms of sentient beings. Those born from the womb are viviparous, which mainly refers to mammals that modern people refer to, such as humans, elephants, horses, cows, pigs, sheep, and donkeys. Those that are born from eggs and emerge from the egg shell are oviparous. For example, geese, geese, chickens, ducks, and fish are oviparous animals. Moisture-born organisms are organisms that can grow in water and can grow in the presence of water. They are not viviparous or oviparous. Metabiosis is another life form. For example, if grains are stored for a long time, insects will naturally grow. They can only be born from moisture, which is called moisture-born, such as flying insects, moths, mosquitoes, flies, centipedes, dragonflies, etc. Or according to the dung collection, or according to the filthy toilet, or according to the carrion, or according to the old porridge, or according to the clump of grass, or according to the thick forest, or according to the grass hut, or according to the leaf cave, or according to the pond or marsh, or according to the wetland of rivers, lakes and seas. wait. Metamorphosis means to be born suddenly from nothing. That is, it has nothing to rely on and appears through karma. Such as heaven, hell, and part of the ghost species.