In one respect at least, eggs are the most remarkable of animal cells: once activated, they can give rise to a complete new individual within a matter of days or weeks. No other cell in a higher animal has this capacity. Activation is usually the consequence of fertilization—fusion of a sperm with the egg. In some organisms, however, the sperm itself is not strictly required, and an egg can be activated artificially by a variety of nonspecific chemical or physical treatments. Indeed, some o...
