Source : Webster's Revised Unabridged Dictionary (1913)

Hectocotylus \Hec`to*cot"y*lus\, n.; pl. {Hectocotyli}. [NL.,
   fr. Gr. ? a hundred + ? a hollow vessel.] (Zo["o]l.)
   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.

Source : WordNet®

hectocotyli
     See {hectocotylus}