internally
A platypus mates internally.
externally
internal
That depends on the species you are asking about, mammals fertilize internally and fish externally.
Guppies are fertilised internally they are livebearers.
Amphibians fertilize their eggs externally.
Koalas do not fertilize their young. They fertilize each other (internally) to produce young.
A deer is a mammal, so reproduction is done internally.
true
Internal fertilization
No. Fishes fertilize externally.
Fish and amphibians are two groups of animals that typically fertilize externally. They release their eggs and sperm into the water to fertilize externally rather than internally.