“…Send not to know for whom the bell tolls; It tolls for thee.” All right, so 17th century English poet John Donne didn’t have the gargantuan U.S. mutual fund industry in mind when he penned those words. But that doesn’t mean that at least some mutual fund managers and their bosses won’t be watching uneasily tomorrow as the an exchange-traded fund (ETF) version of the Pimco Total Return Fund (PTTAX) makes its debut.