Camera lucida sketches of the zebrafish embryo at selected stages. This image is in the Blastula period at the 3.3 hour high cell stage. The animal pole is to the top for the early stages, and anterior is to the top later, except for the two animal polar (AP) views shown below their side view counterparts for germ-ring and shield gastrulas. Face views are shown during cleavage and blastula stages. After shield stage, the views are of the embryo's left side, but before the shield arises one cannot reliably ascertain which side is which. Pigmentation is omitted. Arrowheads indicate the early appearance of some key diagnostic features at the following stages: 1 k-cell: YSL nuclei. Dome: the doming yolk syncytium. Germ ring: germ ring. Shield:...