No, the platypus does not fertilise its eggs externally.
No - they fertilise internally.
Cats fertilise internally.
All insects do this.
internally
A platypus mates internally.
internally
eggs to fertilise and sperm to fertilise it
with their bum
The Platypus and Echidna .
Platypus eggs are soft and leathery, rather than hard-shelled.
Platypus lay eggs.
The egg shell is formed withing the hen and although somewhat porous, not enough for sperm to enter. Fertilization takes place between the ovum and sperm prior to the formation of the completed egg.