A lot vs. Alot: 9 Grammatical Pitfalls
ectoderm ec·to·derm (ěk'tə-dûrm')
The outermost of the three primary germ layers of an embryo, from which the epidermis, nervous tissue, and sense organs develop. Also called ectoblast.
The outermost of the primary germ layers of an animal embryo. In vertebrates, the ectoderm gives rise to the epidermis and associated tissues (such as hair and sweat glands), enamel of the teeth, sense organs, nervous system, and lining of the nose, mouth, and anus. Compare endoderm, mesoderm.
the outermost of the three germ layers, or masses of cells, which appears early in the development of an animal embryo. In vertebrates, ectoderm subsequently gives rise to hair, skin, nails or hooves, and the lens of the eye; the epithelia (surface, or lining, tissues) of sense organs, the nasal cavity, the sinuses, the mouth (including tooth enamel), and the anal canal; and nervous tissue, including the pituitary body and chromaffin tissue (clumps of endocrine cells). In adult cnidarians and ctenophores, the body-covering tissue, or epidermis, is occasionally called ectoderm. See also endoderm; mesoderm.