‖n.; pl. Hectocotyli [ NL., fr. Gr. &unr_; a hundred + &unr_; a hollow vessel. ] (Zool.) One of the arms of the male of most kinds of cephalopods, which is specially modified in various ways to effect the fertilization of the eggs. In a special sense, the greatly modified arm of Argonauta and allied genera, which, after receiving the spermatophores, becomes detached from the male, and attaches itself to the female for reproductive purposes. [ 1913 Webster ]