-1]4- general pattern is that noted above. This species of rats is essentially herbivorous; they obtain their food from the land plants, seeking out and eating the seeds of grasses, sedges, sand burrs, and leaves of some of the succulent plants. The plants upon which the rats feed concentrate 5r90 and Cs!37, These radioisotopes account for approximately radioactivity within the organs of these 100 percent of the animals except immediately after shot,when additional short lived radioisotopes are also present. During this time, 1!33, 1131 may be present in very high levels in the thyroids. By following the pattern of gross radioactivity it has been possible to delineate the broad trends in the distribution of materials in an atoll and its surrounding area. radioactive There. remains much that can profitably be done to amplify this study, but enough is now known to point the need for increased the distribution of specific isotopes. attention to the task of following Thus, more can be learned about selective absorption of elements by different organisms, and an unparalleled opportunity is presented to study the role of trace elements in the marine environment. In the remote atolls of the Marshall Islands important contributions to biology have been made; the need now is to apply the mowledge, techniques and skills to increasing the productive capacity of our freshwater areas. There is every evidence that the rewards in increased