Age, 21.9 days.

Standard length, 5.69 mm.

Length of caudal fin, 1.76 mm. Mesencephalon width, 1.18 mm.

Birth usually takes place at this stage, as the embryos rupture the follicle walls and move into the ovarian cavity and into the gonoduct. The remaining yolk is completely enclosed within the abdominal cavity, but is still visible through the thin belly epidermis. The heart has now assumed its definitive position, with the sinu-atrium situated poste-rior to the conus and ventral aorta. Growth after birth is rapid, and the larval fish in-creases to almost 7 mm. within 24 hours after parturition. Macromelanophores in the wild stock of platyfish do not appear until one or more days after birth, so that only micro-melanophores are present at stage 26.