I was partly referring to Brett's pic, but also to Joe's text. Sorry for creating confusion, gentlemen.
To continue about the gas masks:
Well Joe, I have zoomed in and I have come to the conclusion that it must be an April 1915 model. But I can still not understand well those elastic straps, which look quite uncomfortable (watch the ear!) and like almost self-produced. Confusing and confused by the straps and not the by me expected strings.
I show you a detail and afterwards the complete picture of a Bavarian Jager, somewhere in the Vosges in 1915, showing an April 1915 model gas mask. The mask contained a tissue, drenched in hyposulfite, according to the example of the French C1 Model.
I also found on the same page this perhaps interesting photo, showing a 1914 Draeger Model on the left, and an August 1915 Gummimaske Model.
The Draeger gas mask was quite complex; top a cartridge with Calium (?), centre a container with compressed oxygen and an air tight sack below. It was a closed circuit, and could work for an half hour. It was mainly handed to medics, sappers, and sentries in observation posts. Perhaps because it was so difficult to handle?