A comparison of the activity in different organs of crabs was made using the court found in muscle as unity. relative to muscle for other tissues respectively were: The values in pre and post test crabs digestive system, 6 and 30; gills, 3 and 22; and exoskeleton 6 and 16. In 40 comparisons of the shell and soft parts of pre-test molluscs, the shells were more radioactive than the soft parts for 25 percent,and for the other 75 percent the reverse was true. Post Test Invertebrates collected after Mike test are listed in Table & of the Appendix. Limitation of time made it impracti- cal to search thoroughly for specimens that would have made possible a complete comparison of collection stations accord- ing to species. the shot Since the collections were made soon after (2 to 8 days) it may be presumed that the-distribu- tion of radioactive materials was still ina state of flux in the waters of the lagoon, with consequent variability in the degree of radioactive contemination even between local areas at a given station. The specific activity of individual samples of invertebrates ranged from background at Japtan to 15,000,000 d /m/g wet (sand from sea cucumber gut) at Engebi. One exceptional piece of coral detected from an autoradiograph (Fig.22b) had @ specific activity of approximately 100,000,000 a/m/e. Analysis by Area. Differences in activity between or- ganisms at various collecting stations depend upon the species - 36 - cae BO?