1.- Sexual reproduction and fertilisation

Most animals reproduce sexually: a new individual is created by the fertilisation of a female ovum by a male sperm.

In nearly all species of animals, individuals are either male or female. They can be distinguished by their reproductive systems:

- Males have testicles, which produce sperm.

- Female have internal ovaries, which produce ova.

Males and females can also be distinguished by differences in their size and colour.

In some animal species, an individual can be both male and female. They have both testicles and ovaries. These animals are called hermaphrodites. Snails and earthworms are hermaphrodites.

Sexual reproduction in animals