- Internal fertilization
Internal fertilization is a form of
animal fertilization of anovum byspermatozoon within the body of an inseminated animal, whether female or hermaphroditic. This is distinct from external fertilization, where the union of the ova and spermatoza occur outside of theorganism .In
mammal s, internal fertilization is done through copulation, which involves the insertion of thepenis into thevagina . Some other highervertebrate animals (mostreptile s, mostbird s, and somefish ) reproduce internally, but their fertilization iscloaca l.The union of spermatazoon of the parent organism. At some point, the growing egg or
offspring must be expelled. There are three general ways of doing this:* Oviparous organisms, including most
insect s and reptiles,monotreme s, and all birds lay eggs that continue to develop after being laid, and hatch later.* Viviparous organisms, including almost all mammals (such as
whale s,kangaroo s andhuman s) bear their young live. The developing young spend proportionately more time within the female's reproductive tract. The young are later released to survive on their own, with varying amounts of help from theparent (s) on thespecies .*Oviviparous organisms, like the
garter snake , and theMadagascar hissing cockroach , have eggs (with shells) that hatch as they are laid, making it look like "live birth".
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