In sight seeing in Paris, Twain visited some of the faubourgs and speculated that some of the residences belonged to "lorettes". I guessed the innuendo correctly.
From the Internet:
"The middle ground between street prostitute and grand dame of commercial sex, the courtesan, lorette became an umbrella term for the kept women set up discreetly in a private apartment by a businessman, professional, or wealthy student... Always elegantly dressed, the lorette peeps out coyly from a theatre box, engages in double entendre with male admirers at a masked ball, displays herself while enjoying the view from her apartment window... the lorette slid imperceptibly across the boundaries of acceptability and social stigma."

-Nicholas Green, The Spectacle of Nature

The lorettes were named for the church of Notre Dame de Lorette which was the church close to the distict where they lived and which they attended.

Dear dxb: so professional reporter Clemens didn't do his homework. Thanks.