The importance of this film, which is silent and in many respects a little out-of-date in technique, lies both in the shots taken during professor Johannes Schmidt's famous 'Dana' expedition, and in the fact that it describes his discoveries about the migration of eels. He proved that the mature eel makes its way to the depths of the Atlantic to produce its fry. He also demonstrated that the young eels make their way back to fresh water round the East coast of the Atlantic.
Filmen er med engelske mellemtekster. Den findes også med danske mellemtekster med titlen Aalens Livsmysterium.