ANATOMY

Detailed explanation-1: -After a blastocyst implants in the uterus around the end of the first week after fertilization, its internal cell mass, which was called the embryoblast, is now known as the embryo. The embryonic stage lasts through the eighth week following fertilization, after which the embryo is called a fetus.

Detailed explanation-2: -1. Prototheria (before gestation)-egg laying mammals, 2. Metatheria (middle gestation)-pouched mammals and 3. Eutheria (true gestation)-live birth from uterus.

Detailed explanation-3: -Mammals undergo holoblastic rotational cleavage, characterized by a slow rate of division, a unique cleavage orientation, lack of divisional synchrony, and the formation of a blastocyst. 9. The blastocyst forms after the blastomeres undergo compaction.

Detailed explanation-4: -Blastocyst Development. Soon after fertilization, the embryo is created from a small group of cells that are constantly dividing inside of a complex structure called the blastocyst. Blastocyst Implantation. Embryo Development. Fetal Development.