more tissues rather than on counts of the entire organism, as was done for certain treatments of the fish data. Attempts to compare species by areas on the basis of the ratios of activity of their tissues were thwarted by a lack of some samples and by the presence of many samples with only background counts, i.e., net sample counts of zero. Also, the method of ranking was considered but was believed to be inadequate because of the great effect of surface contamination upon the average of a limited number of sample counts (see p.18). Results. Table 5, page Appendix Table 1 gives individual sample values. 32, shows average amounts of radioactivity in the main invertebrate groups: at the collecting localities. Blanks indicate no specimens were found. out the These values bear inverse relationship of radioactivity to distance from the test sites for operations previous to Ivy, extended from Runit Island to Engebi Island. which Within this range the only significantly low counts came from a small collection made by navy personnel on Piiraai Island. However, it is probable that because of this island's position relative to the prevailing winds, waves, and current it neither initially in spite received nor retained large amounts of radioactivity, of its intermediate position between two shot islands. Igurin and Japtan Islands were almost equally low, and Rigili higher. Because of their marked influence upon the averages, the high-counting samples included in Tabie 5 and Appendix Table are listed separately in Table 6. - 31> a