Neurobiologists have gained new insights into how different types of nerve cells are formed in the developing animal. Through specialised microscopes, they were able to follow the development of the neural retina in the eye of living zebrafish embryos. Using high-resolution three-dimensional time-lapse images the researchers simultaneously observed the division of retinal nerve cells and changes in gene expression. This enabled them to gain insights into the way in which the two processes are linked during eye development and how the number and proportion of different cell types are regulated.