part of part of immediately preceded by immediately preceded by occurrent stage 12 mid-mesenchyme blastula episode late mesenchyme blastula episode All skeletogenic primary mesenchyme cells (PMCs) have ingressed into the blastocoel. Many of these cells have extended filopodia and migrated away from the vegetal plate. The cells are found along the blastocoel wall, although they remain concentrated in the vegetal hemisphere of the embryo. The vegetal plate has flattened following the ingression of the PMCs. However, it has not started to invaginate. It is now composed at its center of the 8 small micromere descendants (the germ line) surrounded by non-skeletogenic mesoderm (NSM). ecao_developmental_stage late-MB