 Complete the following phrase:  In 1685 the Kangxi emperor legalized private maritime trade along the coast, establishing a series of customs stations in major port cities. The customs station at Canton became by far the most active in foreign trade and by the late Kangxi reign more than forty mercantile houses specializing in trade with the West had appeared. The Yongzheng emperor made a parent corporation comprising those forty individual houses in 1725 known as the Cohong system. Firmly established by 1757, the Canton Cohong was an association of thirteen business firms that had been awarded exclusive rights to conduct trade with Western merchants in Canton. Until its abolition after the 