Processes of Localization in Developing Fundulus

Abstract

The method of local vital staining was used to study the early localization of embryonic organs in the blastoderm, and to ascertain the movements by which the cells forming these organs attain their final positions in the embryo. The early embryonic shield includes the material for the nervous system posterior to the forebrain, and the presumptive endoderm; the notochord was not positively located, but the contributing cells are probably situated in the early shield between the areas for endoderm and nervous system. The lateral wings of the shield contain the mesoderm for the head and for the region of the first few somites; the mesoderm for the post, part of the embryo is furnished by the germ-ring. The material for the forebrain and eyes is originally located in the extra-embryonic membrane anterior to the shield, and it enters the anterior part of the shield during gastrula-tion. The material for the eye and forebrain is derived from 1 or 2 of the central cells of the 16-celled stage; the germ-ring is derived from the peripheral cells of the 32-celled stage. In addition, it was shown that the embryonic axis bears no constant relation to the position of the cleavage planes, but coincides most frequently with the 2d.