Your Inner Fish: Chapter 6 The Best-Laid (Body) Plans

Biologists study embryos as the first stage of life. They found that embryos of species like fish, amphibians, birds, and mammals look very similar in the beginning stages of embryonic development. The study of similarities, differences, and development in embryos is called embryology.

Biologists found that there are three layers of tissues in  developing embryos that are responsible for developing all body parts which vary from one species to another. The outer layer is called the ectoderm, the inner layer is called the endoderm, and the middle layer is called the mesoderm. The ectoderm forms much of the body (skins and nervous system). The endoderm forms the inner structures of the body (digestive tract). The mesoderm forms tissues between guts and skin (skeletons and muscles).



DNA control controls how the body is formed. Hilde Mangold discovered a small patch of tissues that was able to direct other cells to form an entire body plan this patch of tissues is known as the Organizer.