This structure implants around one week after fertilization. As development continues, the epiblast invades inward toward the primitive endoderm. This begins the differentiation into the three germ ...

A study published today (September 11) in Nature Ecology & Evolution suggests that instead of two distinct germ layers, cnidarians may indeed have three. The authors show that the mesendoderm of the ...

Identify stage A. Identify stage B. As cells take up new positions during gastrulation, they may receive information from newly adjacent cells that influences their course of subsequent development.