The cultured pearls on the market today can be divided into two categories. The first category covers the beaded cultured pearls, including Akoya, South Sea, Tahiti and the large, modern freshwater pearl, the Edison pearl. These pearls are gonad-grown, and usually one pearl is grown at a time. This limits the number of pearls at a harvest period. The pearls are usually harvested after one year for Akoya, 2–4 years for Tahitian and South Sea, and 2–7 years for Edison. This perliculture process was first developed by the British biologist William Saville-Kent who passed the information along to Tatsuhei Mise and Tokichi Nishikawa from Japan.