Hec·to·cot·y·lus n.; pl. Hectocotyli   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.

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