Also found in: Dictionary, Encyclopedia, Wikipedia.


The central portion of the ovarian complex of trematodes and cestodes in which fertilization takes place and the vitellarian or eggshell materials are coated over the egg; this occurs in a rapid, stamping-mill sequence, after which eggs pass into the uterus for tanning of the shell, storage, and passage toward the genital pore.
[G. ōon, egg, + typos, stamp, print]