This is a dorsal section through a zebrafish embryo during gastrulation showing neurectoderm tissue (cell nuclei in cyan and cell membrane in magenta) and underlying mesendodermal tissue (green cells) ...

Five zebrafish embryos in a tiny drop of water. The yolk sac is clearly visible, with the first two cells located at its tip. Hair, nails, and horns, all made up of keratin, are some of the hardest ...