John Philip Trinkaus - Trink's work on the Yolk Syncytial Layer (YSL) in Fundulus Epiboly

One of Trinkaus’s first successful series of experiments on Fundulus helped establish the yolk syncytial layer’s (YSL) role in epiboly during gastrulation. The YSL is comprised of multi-nucleated yolk cells, positioned around the edge of the blastoderm, and it is continuous with the thinner yolk cytoplasmic layer (YCL). The blastoderm is the cellular cap of the embryo composed of an outer monolayer of epithelial cells (the enveloping layer, or EVL), and an inner mass of deep cells (see diagram).