Fig. 3. Perfusion coefficients of wild-type mouse embryos. Plasma flow magnitude in the early capillary network was determined between the 3- and 8-somite stages by calculating a perfusion coefficient using FRAP. Each measurement is plotted and three measurements were made from each embryo. The total number of embryos analyzed is indicated for each stage. The upper range of perfusion coefficients increases as cardiogenesis progresses and at the 6-somite stage and later, flows that are too fast to measure are observed (asterisk and arrow). We observed a range of values even within a given embryo because flow naturally varies throughout the highly branched plexus.