Name	Brief description/function	When is it formed?	What is it derived from?	What does it give rise to?	Additional notes
Blastocyst	Mammalian version of blastula; hollow ball of cells that have not yet differentiated into germ layers	Days 1-7 (prior to implantation and gastrulation	Zygote	The embryo	Helps develop trophoblast layer
Inner cell mass	Mass of cells in blastocyst that gives rise to embryo proper (incl. germ layers)	Days 1-7 (prior to implantation and gastrulation	Outer layer of blastocyst cells	The embryo
Trophoblast	Outer epithelium of blastocyst; initiates implantation	Days 1-7 (prior to implantation and gastrulation	Outer layer of blastocyst cells	The placenta	Breaks down endometrium to allow for implantation forms placenta
Epiblast	During gastrulation, epiblast cells form all three germ layers	Around implantation time (7 days after fertilization)	Inner layer of blastocyst cells	The 3 primary germ layers
Hypoblast	Helps orient embryo and primitive streak leading to/during gastrulation	Around implantation time (7 days after fertilization)	Inner layer of blastocyst cells	The yolk sac, the allantois, and the embryonic endoderm
Extraembryonic membranes	Chorion; allantois; amnion; yolk sac. See PART 1.	Around implantation time (7 days after fertilization)	Trophoblast, epiblast, and endometrial tissue	N/A	Form the ‘life support’ system of the embryo
Placenta	Mediates gas exchange, nutrient exchange, waste disposal b/w embryo and mother	After implantation (10-11 days after fertilization)	Trophoblast, epiblast, and endometrial tissue	N/A	Gas exchange and provides nutrients

Name Brief description/function When is it formed? What is it derived from? What does it give rise to? Additional notes Blastocyst Mammalian version o