n, pl  -y*ses   1  :  one of the slender sterile often septate filaments of many cryptogamic plants (as fungi) that are borne among the spore- or gamete-forming organs, are single or branched, and are composed of one or more cells  2  :  a median evagination of the roof of the telencephalon anterior to the epiphysis of certain lower vertebrates that is present only in the embryo of higher vertebrates .
 
 
 
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