The one sure thing about the Seven Sisters is that each school is sure that the other schools are full of brain-dead sluts. “Bryn Mawr to wed, Smith to bed, and Wellesley to talk to” was an old saying when I was there. Alter at will.
The Seven Sisters were:
Wellesley
Smith
Mount Holyoke
Radcliffe
Bryn Mawr
Vassar
Barnard
and were basically the female Ivy League. Remember that women were not allowed into most Ivies until the late sixties and early seventies; and that these schools were THE places for ambitious women to go. They were always a lot more diverse in social and economic class than most people think (OK, so there were quotas on Jews and Catholics and blacks, but usually not outright bans) and studies have shown that women’s college grads are more successful than their co-ed counterparts (although I suppose this is changing now that we can even go to the Citadel and stuff). I went because of the financial aid package and because of the courses, not because it was women, but later realized it was so damn nice NOT to have to worry about being the first woman this or that, or having the guys hog the class time, or the science labs, or get all the nice gym equipment… 
I think there’s probably Seven Sisters for the South and/or Western older women’s colleges, and a Catholic system for ones like Emmanuel and Regis. BTW, Vassar has “gone under”, as we called it, by going co-ed, Barnard and Radcliffe were formed just because women weren’t allowed into Columbia and Harvard, and Radcliffe doesn’t really exist anymore as a separate entity. So now there’s technically five sisters. There’s some very famous women’s colleges, like Wheaton in MA, Spellman in GA, and Mills in CA, that aren’t on the classical list.
I think Oberlin was the first college to be co-ed, in the 1860’s.
Not that you asked, but Wellesley and the other two ones in MA, Smith and Mount Holyoke, are doing fine staying all-women and have more applicants than they can handle, so I don’t think any of us will “go under” soon.
Maybe I should start another thread for us ladies who went to these nice but sometimes odd places, on their weird customs and phrases. Ask me if the men in our dorms were allowed to move horizontally, vertically, or both…