The variability that may be expected from two collec tions taken in close proximity is pointed out in the comparison of two collecting areas on Engebi. Tide pool collecting at the west tip on the lagoon side yielded invertebrates containing significantly less radioactivity than did those collected on the outer, north shore. The average of all samples as well as counts of comparable tissues were alike in this respect. See Table 1 in the Appendix. The relationship of radioactivity to animal group is not soaltar as it is to locality. Comparison with 1949 findings at Eniwetok shows mutual tendencies toward high activities in samples of hydroids, sponges, starfish, and oysters, in descending order of magnitude, with crustaceans and corals conta ining relatively little radioactivity. Table 7 gives frequencies of counts by magnitudes for the major collecting areas for both pre and post shot material exclusive of dredged samples. The trend for high counts to predominate near shot areas is almost the same both pre and post test. Table 7 also serves to demonstrate that the frequency of distribution of logarithms of counts in the post test series is approximately of the normal form, whereas the distribution of the observed counts would be strongly skewed. In the pre-test series the distribution of the logarithms of the counts is normal only in the "hotter" areas and then only if background counts are excluded. - 34 --