Images of women suspended vertically in transparent capsules captured the imaginations of fantasy writers in the 20th Century.  Above and below, illustrations for the covers of pulp science fiction magazines.

And here's the same idea in a classic Hollywood horror film, The Black Cat:

I guess it's just a variant of the glass coffin in which many a fairytale princess has slept her enchanted sleep:

Originally, I suppose, the image suggested a virginal state, from which the prince's kiss would awaken the maid, a kind of sexual initiation.  I'm not sure what it signifies in the modern age, but probably not that — more likely a vision of woman as pure image or possession, safe, contained, unthreatening . . .