A comparison of the activity in different organ s of crabs was made using the count found in muscle as unity. The values relative to muscle for other tissues in pre and post test crabs respectively were: digestive system, 6 and 30; gills, 22; and exoskeleton 6 and 16. 3 and 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 colleeted after Mike test are listed in Table 2 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 aceord- ing to species. Since the collections were made soon after the shot (2 to 8 days) it may be presumed that the-distribu- tion of radioactive materials was still in a state of flux in the waters of the lagoon, with consequent variability in the degree of radioactive contamination even between local areas at a given station. ; fhe specific activity of individual samples of inverte- brates 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 a@ specific activity of approximately 100,000,000 d/m/g. Analysis by Area. Differences in activity between or- ganisms at various collecting stations depend upon the species - 36 -