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Related to ectoderm: mesoderm


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.
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The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



(1) The outermost germ layer; the external layer of the embryo of multicellular animals in the gastrular stage. From the ectoderm are formed the integuments, nervous system, sensory organs, anterior and posterior sections of the digestive tract, external gills, and ectomesenchyme. In the Deuterostomia, all the elements derived from the ectoderm are formed as a result of the action upon it of the chordomesoderm, the entoderm, and their derivatives.

(2) The external wall of the body of coelenterates. The ectoderm consists of a single layer of cells—epithelial, epithelio-muscular, interstitial, and sensory cells, as well as stinging capsules.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.


The outer germ layer of an animal embryo. Also known as epiblast.
(invertebrate zoology)
The outer layer of a diploblastic animal.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
References in periodicals archive ?
The binary character model allows an assessment of the history of any structural elaboration of ectoderm between the post-oral arms and does not distinguish between degrees of elaboration.
Sp-Smad2/3 mediates patterning of neurogenic ectoderm by nodal in the sea urchin embryo.
Namely, Wnt6 is expressed in the neural plate border at the onset of neurulation (E4) and in the dorsolateral edges of the forming neural tube at E5 (neural crest progenitor region), whereas Wnt8 is absent from a neural plate border at E4 but at E5 is expressed in the non-neural ectoderm, directly adjacent to the neural crest progenitor region.
of cases Percentage Post auricular 2 33.3% Parotid 2 33.3% Pre auricular 1 16.7% Over the maxilla 1 16.7% DISCUSSION: Epidermoid are derived from ectoderm, but they are inclusion cysts that are lined only by squamous epithelium.
In Physalia, the cnidosacs are more hemispherical and the ectoderm thinner than Porpita.
After formaldehyde was applied, a fluorescent stain appeared in cells of the ectoderm or at their surface.
But he believes that other genes may possibly serve as markers for selecting lines primed for mesoderm and ectoderm development.
This value corresponds to the thickness of the anal plate ectoderm. The relationship between the degree of invagination and the position of the boundary is shown in Figure 4.
Within the larva, a new nervous system forms from the ventral ectoderm in close proximity to the water vascular system (MacBride, 1907; Narasimhamurti, 1933; Olsen, 1942).
Cholesteatoma or epidermoid cyst is a cystic mass-like lesion originating from the aberrant ectoderm trapped within the petrous apex.
The embryological development of the human eye involves a series of events, beginning with fertilization of the ovum and continuing through the early postnatal period, in three embryonic layers: neural ectoderm, neural crest, and surface ectoderm, with minor contribution from the mesoderm.
These glands develop from an early structure called the oral ectoderm, but the actual process is not fully understood.