Source: Human Fertilization image, Creative Commons: http://commons.wikimedia.org/wiki/File:Human_Fertilization.png; Blastocyst image, Creative Commons: http://commons.wikimedia.org/wiki/File:Blastocyst.png
A stage of development of an individual formed from the inner cell mass of a blastocyst after it has implanted in the uterus.
A layer of the blastocyst which will develop into an embryo.
After the morula forms it will implant on the endometrium of the uterus; the blastocyst contains an inner of layers of cells that become the embryo while the outer layer of cells form the placenta.
The fertilized egg which is the first cell of an individual.