At this point the zebrafish embryo contains three portions, an epithelial monolayer known as the enveloping layer ( EVL ), a yolk syncytial layer ( YSL ) which is a membrane-enclosed group of nuclei that lie on top of the yolk cell, and the deep cells ( DEL ) of the blastoderm which will eventually form the embryo's three germ layers ( ectoderm, mesoderm, and endoderm ).
