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• 0 Days Fertilisation

• 1 Day Cleavage of cells has begun. Day ends with 4 cells present

• 2 Days
• Formation of Morula

• 3 Days Compaction of morula. 16-25 cells within same sized morula.

• 4 Days Blastocyst formation

• 4.5 Days Implantation and invasion into the uterine epithelium

• 5 Days Embryoblast and trophoblast formation. Endometrial reaction occurs

• 6 Days Embryoblast begins to divide into embryonic and extramembryonic cavities. The proamniotic cavity also starts to form. Trophoblast cells also begin to differentiate

• 6.5 Days Axis of embryonic germ disc is defined. Uterine reaction (decidual reaction) occurs.

• 7 Days Formulation of amnion occurs. Formation of mesoderm, entoderm and endometrium also occur.

• 7 ½ Days Closure of the amnion. The neural plate is clearly delimited anteriorly and laterally. The head process is now developing. Foregut development begins. Blood islands develop in the wall of the yolk sac.

• 8 Days Embryo has 1-7 somites present. Progressive deepening of the neural tube. Circulatory system development begins. Intestinal tract development continues. Central nervous system development begins. Extraembryonic membranes grow and begin to fuse. Yolk sac continues to enlarge.

• 8 ½ Days 8-12 somites present. rotation of embryo occurs. The turning of the embryo occurs.

• 9 Days 13-20 somites present. Turning of the embryo has completed. Central nervous system development occurs. The circulatory system and intestinal tract development continues. The urogenital system development begins. Placenta development begins.

• 9 ½ Days 21-29 somites present. The embryo is 1.8-3.3 mm. Cardiovascular, CNS, Intestinal and urogenital development continue. Condensation of forelimb bud occurs.