:Our article primitive groove uses this term, mostly because it is a pathetic sentence cribbed from a century-old encyclopedia.
2.
The primitive groove forms as a depression in the primitive streak as it is developing, and allows a space for migrating cells to move into the deeper layers of the embryo.
3.
PubMed gets a whole six hits for " primitive groove ", which I ought to read later; " blastophore " gets one hit that is about a parasite and clearly not relevant.