AnimalisticZygoteThe process of maturation and production in the uterus of female animals is called fetal birth.embryonic developmentThe nutrients needed can be obtained from the mother until birth.
The embryo passes throughplacentaandumbilical cordTo suckNutrientsAnd oxygen, while sending metabolic waste into the mother body.After the fetus develops in the mother's uterusbirth canalDirect output.
adjective,attributive word。The larva of human or some animals does not leave the mother until it has developed to a certain stage in the mother. This reproductive mode is called viviparity.Embryonic development of viviparous animals depends on maternal nutrition.
vertebrateThe higher groups of middle mammals, such as monkeys, tigers, cattle, sheep, wolves, etc., are all born at birth.
Exceptions:African viviparous toadyesTanzaniaA peculiar genus of toads.Some species under it have very unusual reproductive characteristics.They are all viviparous and the only ones in the world that do not lay eggsToad。
The fertilized eggs of viviparous animals are usually very smallFallopian tubeThe upper end completes fertilization, and then develops into an early embryo, which is implanted into the uterus, and then grows in the inner wall of the mother's uterusplacenta(Placenta) connects with the mother, absorbs nutrients and oxygen in the mother's bloodcarbon dioxideAnd wastes are delivered to the mother's blood and discharged through the mother.When the fetus is mature,Uterine contractionExpel the larva from the body to form an independent new life.Mammalian divisionplatypus、EchidnayesOogenesisOther animals are viviparous.
Viviparous evolutionary history
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Fetal birth refers to the birth from the mother to the fetus. For example, human beings are born after completing their bodies in the mother to the fetus, which effectively guarantees the next generationsurvival rate, mostmammalThey are all born at birth, yessexual propagationA form of allogeneic reproduction.
The process in which the fertilized egg of an animal develops in the uterus of the animal body is called viviparity.The nutrients needed for embryonic development can be obtained from the mother until birth.
significance
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Fetal birth and lactation ensure higher offspringSurvival rate。Fetal birth provides protection, nutrition and stable temperature for developing embryosDevelopmental conditions, which can ensure the normal operation of enzyme activities and metabolic activities, and minimize the external environmentenvironment conditionyesembryonic developmentAdverse effects.And in the uterusamniotic fluidIt can reduce the impact of vibration on the fetus.
