Internal fertilization

Internal fertilization is the union of an egg and sperm cell during sexual reproduction inside the female body. Internal fertilization, unlike its counterpart, external fertilization, brings more control to the female with reproduction. Most taxa that reproduce by internal fertilization are gonochoric.

Male animals inseminate females in order to internally fertilize their egg cells. Most reptiles and certain other vertebrates transfer sperm through a male intromittent organ into the female cloaca during copulation. Mammals ejaculate sperm and seminal fluid through the male penis into the female vagina. Most birds use the "cloacal kiss," pressing cloacas together to transfer sperm. Salamanders, spiders, some insects and some molluscs undertake internal fertilization by transferring a spermatophore, a bundle of sperm, from the male to the female. After fertilization, embryos develop in eggs in oviparous species or inside the mother’s reproductive tract in viviparous ones.

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