What is written up everywhere in hell?

The proverb birds of a feather is written up everywhere in hell—

Spirits follow it out naturally—people here have an exquisitely developed instinct that helps them to judge, in a moment, of those they meet, aided by the transparency of clothes. It is, of course, not quite easy here to carry out such principles—still, society manages very generally to keep itself to itself. 

They eschew vulgarity and turn their back upon anything likely to shock their notions of good-breeding.