Massive database traces mammal organ development, cell by single cell
(PHYSorg.com Biology)

The very early days of growth, long before we are born, are a time of incredible development. In a relatively short period of time, we and other mammals create our bodies` dozens of different organs from a few thin layers of cells. In mice, that period is only four days long. In humans, it`s complete before the end of the first trimester of pregnancy.