Source : Webster's Revised Unabridged Dictionary (1913)

Acephalocyst \A*ceph"a*lo*cyst\, n. [Gr. 'ake`falos without a
   head + ky`stis bladder.] (Zo["o]l.)
   A larval entozo["o]n in the form of a subglobular or oval
   vesicle, or hydatid, filled with fluid, sometimes found in
   the tissues of man and the lower animals; -- so called from
   the absence of a head or visible organs on the vesicle. These
   cysts are the immature stages of certain tapeworms. Also
   applied to similar cysts of different origin.