- 13- are given. The amount of wi85 based on volume is highest in plankton from station 3 rather than from station 38, which contained the highest level based on dry weight of plankton. The values based on dry weights are probably more accurate thanthose based ou vuiuume because of errors in volume determination and variation in plankton species between samples, which result in different volume to dry weight ratios. During the three-week interval following the Collett survey, the station at which the highest values for plankton were found had shifted 150 miles westward. If this shift represents the movement of the water mass, it is a net advance of 7.3 miles per day and is a close approximation of the known westward movement of the water in this area. At the end of three weeks the center of high activity was again sam- pled for water and plankton. No wi85 was found (Fig. 4). Plankton collected at two stations just north of Ujelang Atoll contained 280,000 c/m/g dry weight of wi85. which was also detected on soil, This isotope, plant and animal samples taken at Ujelang Atoll, will be discussed later, Plankton samples collected half way between Bikini Atoll and Rongelap Atoll contained 21,000 d/m/g dry weight of wid, The isotope was also found in samples from Nan Island at Bikini and from Rongelap Atoll. | (ye ce 3, SE or