Definition of "ectoderm" [ec•to•derm]

• The outermost of the three primary germ layers of an embryo, from which the epidermis, nervous tissue, and, in vertebrates, sense organs develop. (noun)
• The outer layer of a diploblastic animal, such as a jellyfish. (noun)

American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.

• "Both the skin and the brain are derived from the same embryonic tissue, which is known as the ectoderm."
• "The outer layer of this ‘gastrula’ is called the ectoderm, the inner layer is the endoderm, and there are also some cells thrown into the space between the ectoderm and endoderm, which are called mesoderm."
• "Thus a portion of the upper marginal zone of the blastula or early gastrula, or else a piece of the roof of the archenteron of the mature gastrula was planted in the blastocoele of a young gastrula and so brought beneath the ectoderm from the beginning; it was demonstrated that these portions were able to induce neural plate."