ectoderm

ectoderm, layer of cells that covers the surface of an animal embryo after the process of gastrulation has occurred. This outer layer, together with the endoderm, or inner layer, is present in all early embryos. In the development of animals of the phyla Porifera, Ctenophora, and Cnidaria, these two primary layers give rise to all the tissues and organs of the animals, a process known as diploblastic development. In higher animals, such as those of the phyla Echinodermata and Chordata, a third, middle layer, the mesoderm, is formed between the ectoderm and endoderm during gastrulation, and the process is termed triploblastic development. In most embryos, differentiation of ectodermal tissue gives rise to epidermis and its specialized structures (scales, feathers, nails, and hair); some exocrine glands (sweat and sebaceous glands); some endocrine glands (the pineal body and the pituitary gland); the nervous system; and the organs of special sense (ear and eye). In animals of some phyla, such as the Mollusca and Annelida, the fate of particular cells of the embryo is determined in the earliest stages of the fertilized egg and may even be fixed at or before fertilization.

The Columbia Electronic Encyclopedia, 6th ed. Copyright © 2012, Columbia University Press. All rights reserved.

More on ectoderm from Fact Monster:

  • endoderm - endoderm endoderm , in biology, inner layer of tissue formed in the gastrula stage of the ...
  • embryo: Developmental Stages - Developmental Stages Among humans, the developing young is known as an embryo until eight weeks ...
  • epithelium - epithelium epithelium , sheet of tissue that covers or lines the external and internal body ...
  • polyp and medusa: Anatomy - Anatomy The two forms are similar in construction; both consist of a cylindrical body surrounding a ...
  • coelom - coelom coelom , fluid-filled body cavity, found in animals, which is lined by cells derived from ...

See more Encyclopedia articles on: Cell Biology