Zebrafish embryos are beautifully transparent, which allows us to follow their development from a fertilised cell to a swimming larvae. In the movie 4 embryos have been filmed over 24 hours. The cells divide repeatedly to form a ball of cells, which is perched on top of the yolk ball that provides the nutrients for the developing embryo. After a few hours a layer of cells moves inside the others in a process called gastrulation. The muscles start to form and become active after around 18 hours - this is when the embryo starts to twitch. The developing eye can also be seen by the end of the movie.
