I rather like this illustration I ran across in some reading. It’s a bit risqué, and reminded me of some ukiyo-e…the kind of thing you don’t usually expect to find in a biology journal.

This line drawing was made from a photograph of a male H. lunulata (shaded) copulating with a female. The arrow points to the male’s hectocotylus, which is being inserted into the female’s mantle cavity.