It's called gastric brooding and several species of now-extinct frogs employed the strategy. The mother frog would swallow her eggs and keeps them in her stomach through the tadpole and early frog phase.
Eventually, she would vomit up, sometimes projectile vomit, a stomachful of babies. Scientists interested in the unique physiology of these frogs are attempting to bring some back from the dead through cloned embryos. [Insert cliché horror line here.]
Thumbnail: Public Domain, Note: Not a baby-vomiting frog.