for the variance considerably impairs the reliability of results. In view of these considerations, the best estimate of" the absolute value of the redioactivity 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 was limited, the most that can be obteined from these data is 4.1 trends and certain relative vaiues. 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 collecting 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 & Foerst-type water bottle. Sample Freparation. Since it was impractical to bring six~liter water samples to the laboratory for processing, a 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 POF AR Here 4