Most animal cells are very small, and most cannot be seen without a microscope; in fact, most cells are smaller than the period at the end of this sentence. Two exceptions are bird and frog egg cells—both are larger cells readily observable with the unaided eye. For example, the chicken egg is actually one single cell—the nucleus, cytoplasm, and cellular membrane, which contains an abundance of yolk and albumin—the nutrients needed for the developing chick (embryo)—making this cell much larger than the normally functioning cells within the chicken.