The 26 venture-backed companies that had IPOs on U.S. exchanges in the second quarter raised a total of $4.27 billion, doubling the amount raised in the same period a year ago, according to the National Venture Capital Association. However, the group also said that merger and acquisition activity declined substantially from last year. Only 67 M&A deals were completed this quarter, while 95 were made a year ago. Life sciences firms accounted for a plurality of the IPO dollars raised, followed by semiconductor and Internet firms.