were chalky looking and lacked even the slight hyaline luster characteristic of most inactive sand particles. One of the larger of these, as well as the sand sample and autoradiograph by means of which it was located, are shown in Figure 18. Autoradiographs of plates of ashed biological samples were made to compare the nature of the distribution of the activity found in these specimens with that of the Engebi and Biijiri sand samples (see Fig. 19). Activity of the tissues with ab- sorbed radiation was diffuse. For those tissues with possible “surface” contamination the distribution of activity was spotty and similar to the sand samples. (Fig. 20) Photographs of the plates show that the ash 1s evenly distributed and that the unexposed portions of the autoradiographs are not due to the absence of ash. Plankton. The spots on plankton autoradiographs from samples dried on filter paper were associated primarily with a white, amorphous material of cheesy consistency, which may be the counterpart in the water of the chalky material in the sand. The autoradiographs also showed some activity associated . with organisms. However, almost every kind of organism that showed activity in one individual would in another case fail to show it. Thus, among foraminifera, gastropods, mysids, and other crustacea there could be found some radioactive and some non-radioactive individuals. to mass of organisms. Activity tended to be proportional This suggests that minute particles sus- pended in the water, or possibly even a certain amount of dis~ 88 -