The Collaborative International Dictionary of English v.0.48:

Lemniscus \Lem*nis"cus\ (l[e^]m*n[i^]s"k[u^]s), n.; pl.
   Lemnisci (-s[imac]) n.[L. See Lemniscata.] (Zool.)
   One of two oval bodies hanging from the interior walls of the
   body in the Acanthocephala.
   [1913 Webster]