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A single unit looks like this. It is handmade(!) from 0.5 mm thick Vivak plastic sheets. The bottom is styrofoam. The labels were printed on normal office transparencies and glued to the unit with a common gluestick.

The Vivak sheets are actually flat and transparent enough that it is quite possible to examine flies from the side with a stereo microscope without removing them from a unit! We've tought about ways to make also the bottom as transparent, but that seems next to impossible (and the labels would obscure then ventral view in any case :))