What is "redias"

Redia \Re"di*a\ (r?"d?*?), n.; pl. L. Redi[ae] (-[=e]), E. Redias (-?z). [NL.; of uncertain origin.] (Zo["o]l.) A kind of larva, or nurse, which is prroduced within the sporocyst of certain trematodes by asexual generation. It in turn produces, in the same way, either another generation of redi[ae], or else cercari[ae] within its own body. Called also proscolex, and nurse. See Illustration in Appendix.