Diversity in Living Organisms — Science STD 9 — Question

Birds and reptiles lay large eggs.
The development is direct and entire development of progeny is dependent on the nutrition available through egg only.
Mammals don't lay eggs and their eggs have less yolk which cannot support the development of the foetus.
Hence the development of foetus takes place inside the body of parent usually female parent and then directly young ones are delivered.
Among birds egg of Ostrich is largest and is often claimed as the largest animal cell with weights nearly $1.5 Kg.$ and requires about $50$ minutes to boil it.