zona-pellucidahttp://www.oed.com/dictionary/zona-pellucida_n%3Ftab%3Dmeaning_and_usezona pellucida, n.
First published 1921; not fully revised

zona pellucidanoun

  1. 1841–
    The transparent membrane forming the cell-wall of the ovum in Mammalia.
    1. 1841
      We saw the incipient chorion, when rising from the ‘zona pellucida’ in the mammiferous ovum, to leave a stratum of unappropriated cells behind it on the ‘zona’.
      M. Barry in Philosophical Transactions (Royal Society) vol. 132 116

Originally published as part of the entry for zona, n.

zona, n. was first published in 1921; not fully revised.