A Brief Overview of Salamander Embryonic Development

演化之聲
Mar 13
2 min read

Updated: Apr 10

Here is a video showing the embryonic development of a salamander, illustrating how a fertilized egg gradually develops into a complete organism.

But how does a single fertilized egg transform into an individual? Let me briefly explain the early stages of this process.

At the beginning, the fertilized egg is a single, very large cell. Early in development it divides into two cells. These two cells then divide again, producing four cells. At this stage the cells are called blastomeres. The embryo continues dividing in a sequence of 2, 4, 8, 16, 32, and 64 cells. When the embryo reaches roughly thirty-two cells, it forms a structure known as the morula. After about sixty-four cells, some cells begin dividing at slightly different times rather than remaining perfectly synchronized.

As cell division continues and the embryo reaches several hundred cells, a fluid-filled cavity called the blastocoel forms within the structure. At this stage the embryo is referred to as a blastula. Soon afterward, a specific region of the embryo begins to fold inward, creating an opening known as the blastopore. This inward movement continues until a new internal cavity, the archenteron, is formed. The embryo at this stage is called a gastrula. In protostomes, the blastopore eventually develops into the mouth, whereas in deuterostomes—including humans—it becomes the anus.

（Image source：Abigail Pyne， CC BY-SA 3.0 ）

The gastrula contains three primary germ layers: ectoderm, mesoderm, and endoderm. The ectoderm later develops into structures such as the skin and the nervous system. The mesoderm forms tissues including muscle, dermis, spinal structures, blood vessels, blood, and the skeleton. The endoderm primarily develops into the digestive and respiratory systems.

Afterward, a structure called the neural plate appears on the surface of the gastrula. Its edges rise upward and gradually fold toward the center, somewhat like folding a blanket. During this process the neural crest and neural tube form, eventually developing into the brain and spinal cord. As these structures take shape, the basic body plan of the embryo becomes visible, and development continues toward an increasingly complex form.

In this way, a complete organism gradually emerges.