\Hy"da*tid\, n. [Gr. ?, ?, a watery vesicle under the
upper eyelid, fr. "y`dwr, "y`datos, water: cf. F. hydatide.]
(Zo["o]l.)
A membranous sac or bladder filled with a pellucid fluid,
found in various parts of the bodies of animals, but
unconnected with the tissues. It is usually formed by
parasitic worms, esp. by larval tapeworms, as Echinococcus
and C[oe]nurus. See these words in the Vocabulary.
{Hydatid of Morgagni} (Anat.), one of the small pedunculated
   bodies found between the testicle and the head of the
   epididymis, and supposed to be a remnant of the
   M["u]llerian duct.