upon the minute primaryplauts of the sea, 1t is certain that any catch of zooplankton must include also whatever phytcplankton exist as undigested fodder. Classification of Organisms. Marine zoologists are able to recognize amongst the zo@> on several characteristic modes of acquiring food, and it was found possible to separate the Castle catch into three sorts. The resulling splits admittedly were small, but this was all that the catch afforded. The clasetfications generally used by biologists are as follow: (8) Setal; feeding with the aid of protruding bristles (setae), (R) Rapacious; seizing food agressively, and (T) Tentacular; gathering food by means of tentacies. RESULTS Gross Beta Activity Measurements. Gross beta activities of each type of feede’: are compared in Table 1. An end-window Geiger-Mvuiler counter having a window thickness of 1.4 mg/cm? was used. The organisms vary widely in size and in weight so that activity has been expressed in Table 1 in terms of wet weight as well as in terms of cry weight of orginism. Beta Absorption Analyses. Figure 1 compares the activities from three feeding types in terms of attenuation caused by aluminum filters interposed in front of the counter. A setal feeder and a rapacious feeder were studied as well as samples of fish larvae whose feeding hehit was not classified. The types are identified in Table 1. Beta Decay Characteristics. Figure 2 compares the decay of beta activities in four kinds of plankton; the curves were not normalized in percent of initial activity because their slopes are very similar and their superimposition would cause a confusing graphical picture. GammaSpectra. The gamma spectra of three selected plankton were obtained in the 70-channel gamma pulse analyser of NRDL and two are shown in Figure 3 along with the instrumental background spectrum. It will be noted in Tabi 1 that both organiars are 10 sateenay en timeda VAR AE Re tn AS REG ENA An Fate ee et | ce Rete Rat er Eo cettemar met ane cm me similar water masses in the sense that no differences in the type of zoopiankton might be expected. However, it has been estimated that fallout arrived at Station 6 when this water was about 180 miles from the shot center, whereas the fallout arrived at Station 8 when this water lay about 80 miles from ground zero. Thus the fallout particles at Station 6 likely were finer than those at Station 8. Both points lay more or less along the axis of the computed fallout pattern, Reference 1. The gamma intensity measured by a Geiger detector (submerged but near the surface) at Station Y - 8 was roughly 10 times as high as the intensity similarly measured at Station Y--6. These and other measurements indicate that the Sample Y ~- 8 carne from water about 10 times more active than the Sample Y - 6. There is oceanographic evidence that substantially only Shot 5 contributed to the contamination of the waters from which each sample was taken. oom Characteristics of the Sea Water Masses Involved. Although the two samples were collected many miles apart, there is oceanographic evidence that the samples came from