Results. Table C.1 gives individual sample values. Table 4.5 shows the average amounts of radioactivity in the main invertebrate groups at the collecting localities. Blanks indicate that no specimens were found. These values bear out the inverse relation of radio- activity to distance from the test sites for operations previous to Ivy, which extended from Runit Island to Engebi Island. Within this range the only significantly low counts came froma small collection made by navy personnel on Piiraai Isiand. However, it is probable that because of the position of this island relative to the prevailing winds, waves, and current, it neither initially received nor retained large amounts of radioactivity in spite of its interme- diate position between two shot islands. Igurin and Japtan Islands were almost equally low, and Rigili was higher. Because of their marked influence upon the averages, the high-counting samples included in Table 4.5 and Table C.1 are listed separately in Table 4.6. Table 4.5 —RADIOACTIVITY OF INVERTEBRATE SAMPLES BY ANIMAL GROUPS, PRETEST* & % 253 s & &B e Organism Sponge Worm Hydroid Coral Starfish Urchin and 0.2 0 #02 0 0 0 _ 3 «& « §& 3 $$ a&€ ow&Swi a Aa 10 0.3 0 0.5 0.2 0.04 4 0.7 0.03 0.2 0.2 2 0.5 0.6 06 0.4 0.02 2 a so as SF a@<«#<« eee EEE i 2 & & 2a 48 0.9 48 0.9 0.8 4 0.8 4 2 ~ 3 2 0.30 0.5 4 1 O72 8 0.3 0,02 — 1 173 q 0.3 2 3 sand dollar Cucumber Cr istacean Ga .tropod Bi: aive Cephalopod Tunicate 0 0 0.07 0 0.02 0.04 0.03 0 Of 0.08 0.08 2 5 05 8 0.5 0.08 0.3 1 0.6 0.5 06 1 O07 0.9 0.02 1t 2 5 1 #1 14.67 5 0.1 0.6 0.01 2 1 0.2 0 6 * Measured in disintegrations per minute per gram (x 1000), wet sample. t Dredged samples. The variability that may be expected from two collections taken in close proximity is pointed out in the comparison of two collecting areas on Engebi. Collections from thetide pool 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 (Table C.1). The relation of radioactivity to animal group is not so clear 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 containing relatively little radioactivity. Table 4.7 gives frequencies of counts by magnitudes for the major collecting areas for both pre- and postshot material, exclusive of dredged samples. The trend for high counts to predominate near shot areas is almost the same in both pre- and posttest samples. 32