Table 1.

Glossary of embryological terms (in bold), alternatives often used (in regular font) in various species and their definition as used in this review.

Term and/or Abbreviation	Equivalent (Species)	Description
conceptus		Refers to all tissue derived from the zygote (embryonic and extraembryonic).
embryo	embryo proper	Before gastrulation equivalent to conceptus. From gastrulation stages refers to the embryonic parts of a conceptus that will give rise to the foetus as opposed to the extraembryonic membranes and placenta.
Epiblast (epi)		Derived from ICM, progenitor population of the three germ layers as well as the amniotic ectoderm and primordial germ cells.
Hypoblast (HB)	Primitive endoderm (mouse)	Cells differentiated from the ICM not contributing to the epiblast. The hypoblast will give rise to the inner layer of the yolk sac and, in primates, to extraembryonic mesenchyme.
Inner cell mass (ICM)	Pluriblast (marsupial)	Cells giving rise to epiblast and hypoblast.
primitive endoderm	HB, Hypoblast	Primitive endoderm is an alternative name to hypoblast and not to be confused with true (definitive) endoderm.
Polar trophoblast (pTB)	Rauber’s Layer (e.g., cow, pig, rabbit, horse)	Trophoblast overlying the ICM or epiblast.
Trophoblast (TB)	TE (mouse)	Extraembryonic layer: cells giving rise to the conceptus-derived part of the chorionic membrane and subsequently the foetal part of the placenta.
Trophectoderm (TE)	TB	During blastocyst stages, before overt differentiation, the trophoblast epithelium is often termed trophectoderm.