Is this a propagator? But no ventilation?

Hi all

I have been lucky enough to get my hands on a greenhouse from a relatives house move, with it came a number of items. One is this, which appears to be a propagator but it does not have any ventilation.

I’ve googled the make and wiki says “Breveté SGDG was a French type of patent that ceased to exist in 1968.” but I haven’t been able to find anything with this name that relates to a propagator.

It has two lips at the back and a indent at the front so it seems like the top should lift up. The tray base does have holes that are slightly covered, for drainage maybe?

Has anyone come across this type before? Any advice would be much appreciated, I am loathed not to use it, just don’t know how to do for the best.

Thanks
Tink