External vs. Internal Fertilization

According to Wikipedia:

External fertilization is a form of fertilization in which a sperm cell is united with an egg cellexternal to the bodies of the reproducing individuals. In contrast, internal fertilization takes place inside the female after insemination through copulation.

Example: fish species such as salmon deposit their unfertilized eggs in the substrate and male salmon fertilize them.

In mammals, internal fertilization is done through copulation, which involves the insertion of the penis into the vagina. Some other highervertebrate animals (most reptiles, most birds, and some fish) reproduce internally, but their fertilization is cloacal.

Killer whales

Examples: humans, whales, kangaroos