1. Early Embryonic Development
(Figure 1)
Begins with a (A) zygote (fertilized egg), goes through….
Cleavage- Series of mitotic cell divisions resulting in many cells, becomes….
(B) 2 cell stage, (C) 4 cell stage....
(D) Morula- solid ball of approximately 50 cells, develops into….
(E) Blastula- hollow structure, fluid filled mass of cells, followed by….

2. Early Embryonic Development
Gastrulation- indentation of the blastula to form a 3 layered structure called….
The gastrula (3 layers) (Figure 2)
A. Ectoderm- outer layer- becomes epidermis, tooth enamel, nervous system, lining of mouth and nose
B. Mesoderm- middle layer- becomes skeleton, muscles, excretory system, circulatory system, & gonads
C. Endoderm- inner layer- becomes digestive tract, respiratory tract, liver, and pancreas

3. Later Development Placenta- Umbilical cord-
Exchange structure between the mother and developing fetus
Exchanges of materials between the blood of the mother & the blood of the fetus.
Blood does not mix
Umbilical cord-
Contains blood vessels
Connects the fetus to the placenta