-ll- accumulated none. The metabolism of the living algae, there- fore, had something to do with the uptake of radioactive particles. From decay curves it appears that this activity could be due to one or more of the following isotopes: Ru lS | ar?>, cst37 cel 44 and sr? Radiochemical analyses of this material are in progress. The decay curves also show the same slopes in the algae as in the solutions, indicating no selective uptake by the algae. When cel44 was added to the solution of mixed fission products, uptake by the algae was very rapid. Other experiments with circles of the alga Ulva lactuca and Nereocystis leutkeana, incubated in solutions of mixed fission products from Engebi sand, showed that five per cent of the total activity in solution was taken up per gram of Ulva in 12 days and 10 per cent by Nereocystis in three days. These experiments will be continued. Electron micrographs of the filtered Engebi sand solution were prepared. No particles were found in suspension, showing that there was a true solution rather than a colloidal suspen- sion of the radioactive particles. B. Food cycling experiments with invertebrates In the experiment with the water movement by the horse mussel, Modiolus modiolus, the presence of suspended matter