for the variance considerably impairs the reliability of results, In view of these considerations, the best estimate of the absolute value of the radioactivity of a group of organisms at a collecting station is an average of the values for the individual organisms. However, for comparison of activi- ties by collecting stations the best estimate is made by comparing similar species and tissues. Because the variance both between and within species was often great and the number of samples vas limited, from these data is 4.1 the most that can be obtained trends and certain relative values. Water Samples While the land and reef collections were being made, the “M-boat” that had transported the field crew from the Oakhill to the collecting station was used for dredging, plankton towing, and water colleeting in contiguous waters. Because of the expected difference in specific activity, the volume of the pre-shot water samples was 6 liters and of the post shot samples, 4 liter. The samples were collected with a Foerst-type water bottle. Sample Preparation. Since it was impractical to bring six-liter water samples to the laboratory for processing, 4 precipitation method was used in the field for the pre-shot samples and only the precipitate was returned to the laboratory for counting and analysis. - 19 - The procedure used in the