Placenta
The egg-laying mammals (echidna and platypus) and marsupial mammals produce a type of placenta that provides nutrients mostly from the egg sac, instead of from the mother's blood. It is positioned in the female's body similar to eutherian mammals.  Non-mammals who give birth to live young rather than laying eggs (some snakes and lizards, and even some fish), have also evolved systems of internal development with a placenta-like tissue: these are examples of convergent evolution.