Definition of "placode"

The placodes are localized thickenings of the cephalic surface ectoderm. Each placode is formed from a group of cells which gives rise to a specific organ with a given specialized function.

1974, Herbert Tuchmann-Duplessis, G. David, P. Haegel, Illustrated Human Embryology, Volumes 1-3, Springer, page 94

The neural crest cell bodies become more distant from the placode, but their cell processes permeate the increasingly fibrillar extracellular matrix subjacent to the placode.

1978, Charles Russell Bardeen, Irving Hardesty, John Lewis Bremer, Edward Allen Boyden (editors), The Anatomical Record, Volume 191, A. R. Liss, page 450

Following neurulation, the placodes are first visible as thickenings of columnar epithelium in the non-neural ectoderm, which will go on to form the paired sense organs (olfactory, otic, and lateral line placodes), the lens of the eye (lens placode), the anterior lobe of the pituitary gland (adenohypophyseal placode) and essential components of some ganglia (epibranchial and trigeminal placodes).

2008, Roderick Nigel Finn, B. G. Kapoor, editors, Fish Larval Physiology, Taylor & Francis, page 15