What is the origin of 'sleep tight'?
Read moreOne of the mysteries of the English language finally explained.
Epithelium giving rising to germ cells, especially that lining the seminiferous tubules of the testis; (also) a layer of cuboidal cells covering the free surface of the ovary (originally believed to give rise to germ cells).
Late 19th century; earliest use found in Journal of Anatomy and Physiology. After German Keimepithel.