This is the system proposed by Kodak to the amateur photographer develop his own pictures even without a darkroom. That was in the beginning of last century from 1907 to 1920. The idea can be understood like this: the film in its original spool is protected from light. But it can't be developed in that state because it is thighed spooled. This device transfers it to another spool light protected by the same principle (one layer film and one layer opaque material), but in a loose way so chemicals can get in and touch evenly the emulsion.

One must fit the film inside the wood box (B). That is on the upper right corner in this picture. The black belt that you see coming our of the tank (above) is also placed inside in the manifold on the left (A). Then both are spooled together on the manifold on the center (Y).This is clearly seen in the illustration below taken from: "Comment obtenir de Bonnes Photographies - Guide de l'Amateur Photographe - Publié par KODAK" (no date on it)



A rubber ribon that goes along with the black belt provides 2 or 3 mm space for the deveoper get in. That is the thing shaped like VVVVV seen above. By doing this a new spool is obtained, light thight and ready for development with the metal tank. Like this:



Here in one advertising published in Photo Miniature in September 1914:



Find more information about the Kodak Film Tank and box cameras at:
Box Cameras.com