Presented below we have the story of the embryonic development.
Firstly, a sperm cell fertilizes the egg and implantation takes place in the uterus. At this stage the embryo is made only out of one cell called the zygote. after the implantation cells divide. With each division the number of cells duplicate. At the stage of 16 cells a solid structure called morula forms. Up to this point all of the cells have been dividing equally forming a symmetrical structure, but at this point, the cells start to organize into a fluid-filled blastula. The blastula has an opening, called a blastopore. Further divisions of the cells of the blastula result in the formation of The three germ layers: ectoderm, mesoderm, and endoderm.
These three layers will develop into all of the different tissues and structures of the organism. The first functional organ to form is the heart, which forms around the third week of embryonic development. At his point the heart begins to beat with the embryo’s own blood, often a different type than
the mothers'.
Quickly after that, the nervous system starts to develop and portions of the brain forming the right and left cerebral hemispheres appear. The nervous system is then developed further, formin the structures that will form the 5 parts of the brain. In this process, the cerebral hemispheres become the largest parts of the brain. The embryonic development finishes with the forming of all of the organs and tissues of the organism and the birth.