Organogenesis

Within just one day the fertilized egg develops from a single cell into a complete and autonomous organism consisting of many different organs.

This section deals with the formation of the major organ systems from the cellular blastoderm stage onward.

At the blastoderm stage, the 6000 cells giving rise to all somatic tissues are located as a single cell wide epithelium at the surface of the embryo. Cell lineage analyses have shown, that the three germ layers – ectoderm, endoderm and mesoderm – are already determined at this stage. Thus, a so-called "anlagenplan" or fate map can be pojected onto the embryo.

• The ectoderm differentiates the nervous system, the epidermis, the fore- and hindgut, the salivary glands and malpighian tubules as well as the trachea and the ring gland.
• The two endoderm fractions represent the anlagen of the midgut.
• The mesoderm gives rise to all types of muscles, the fat body, the dorsal vessel, the hemocytes, the lymph glands and the somatic portion of the gonads.
  

The amnioserosa represents an extraembryonic epithelium, it does not contribute to any embryonic tissue and is therefore not assigned to any of the germ layers.

Germ layers (1.2 MB)
Germ layers, interactive (3.2 MB)