Vatican City is home to some of the most famous art in the world. St. Peter's Basilica, whose successive architects include Bramante, Michelangelo, Giacomo della Porta, Maderno and Bernini, is a renowned work of Renaissance architecture.
This is when the baby's brain, spinal cord, heart and other organs begin to form. The embryo is now made of three layers. The top layer â the ectoderm â will give rise to your baby's outermost layer of skin, central and peripheral nervous systems, eyes, inner ears, and many connective tissues. Your baby's heart and a primitive circulatory system will form in the middle layer of cells â the mesoderm.
Human embryogenesis is a complex process that occurs during the first eight weeks after fertilization. The stages of embryogenesis are described in more detail below. Stage 1: The process of embryogenesis begins with an egg or ovum being fertilized by a sperm cell to form a zygote. The zygote is surrounded by a strong membrane made up of glycoproteins, which the sperm has managed to penetrate. The zygote is formed 24 hours after the egg and sperm nuclei fuse.