The 32-round snail drum (or as it was properly known, the trommelmagazin 08) was developed in 1916 to give increased firepower to units armed with the LangePistole 08, or artillery Luger. These pistols were also used by stormtroopers prior to the introduction of the first submachine guns (which, incidentally, were also developed to use these drum magazines).
The drums were generally discarded after the war, as submachinegun development with more typical stick magazines made them obsolete. Today they are fairly rare and valuable, and quite interesting to use. The mechanism inside the snail drum actually uses two discreet mainsprings - one a typical coil spring in the stick portion and the other a flat clock spring in the drum. The lever on the back is used to tension and un-tension the clock spring, and as a result it moves as the drum is fired, until the cartridges stored in the drum portion itself are used up. At that point the coil spring takes over, feeding the remaining rounds in the box portion of the magazine.