...contain some nutrition for an embryo, in contrast to sperm, which normally contain just genetic material and the internal machinery needed for swimming to meet an egg.Bird eggs, however, differ from those of most reptiles in having a hard shell...

...for nutrition. There are also plants that aren't green at all. They lack the green pigment that is part of the internal machinery of photosynthesis, so they depend on other plants for nourishment; in short, they are parasitic. We have several...