Carnegie Stage 7 and 8, gastrulation, migration of cells through the primitive streak to form endoderm and mesodermal layers of embryo.
Carnegie stage 7 embryonic disc viewed from ectodermal (amniotic) surface.
Identify primitive streak, primitive pit and primitive node (of Hensen). Connecting stalk to left.
Carnegie Stage 8 embryonic disc (similar view above).
From the primitive pit (in opposite direction to streak) will extend a fold of ectoderm, the beginning of notochordal process.
Scanning electron micrograph through the streak region showing the early forming 3 layers: ectoderm, mesoderm and endoderm. (from Embryo Images by Dr K.K. Sulik & P. Bream, diagram from Langman's Medical Embryology by T.W. Sadler) (http://www.med.unc.edu/embryo_images/unit-bdyfm/bdyfm_htms/bdyfm003.htm).
Link to next page in this Practical 3 - Notochord