Internal fertilisation is the union of an
egg cell with a
sperm during
sexual reproduction inside the body of a parent. For this to happen there needs to be a method for the male to introduce the sperm into the female's reproductive tract. In
mammals,
reptiles, some
birds, some
fish and certain other groups of animals, this is done by
copulation, the
penis or other
intromittent organ being introduced into the
vagina or
cloaca. In most birds, the
cloacal kiss is used, the two animals pressing their cloacas together while transferring 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. Following fertilization, the embryos are laid as eggs in
oviparous organisms, or in
viviparous organisms, continue to develop inside the reproductive tract of the mother to be born later as live young.