* Animals that develop inside an egg? This includes many animals, such as:
* Birds: Chickens, ducks, eagles, etc.
* Reptiles: Snakes, lizards, crocodiles, turtles
* Fish: Many types of fish, such as sharks, rays, and some bony fish
* Amphibians: Some amphibians, like frogs and salamanders, lay eggs, but others give birth to live young
* Monotremes: The only mammals that lay eggs (e.g., echidnas and platypuses)
* Animals that develop inside the mother's body? This is known as viviparity and includes:
* Most mammals: Humans, dogs, cats, whales, dolphins, etc.
* Some reptiles: Certain species of snakes and lizards
* Some fish: A few species of sharks and fish give birth to live young
* Some amphibians: Some salamander species give birth to live young
To give you a more accurate answer, please clarify what you mean by "develop internally."