I got 66 endrega emryos and still miss fetus. Anezka sell only endrega teeth (what for I wonder?). Quest stuck on 3/4...
Dude... the embryo is
the fetus. You're missing another item, most likely the arachas eyes - they can be bought from Cedric, or dropped by the Arachas you fight later on in the chapter.
As for the embryo, yes, they do drop from Endregas, quite frequently in fact. These enemies don't disappear from the forest once you've killed the queens, and can be found here and there. A good place to start looking is around those eggs you destroyed, or around the altar of Veyopatis.
Right... for some reason Troll tongue disappiared from my inventory. Nevertheless, since 1.2 Cedric sell all except embryos for that quest.