1. Studies with radioactive tracers show that the nemertine Lineus ruber actively accumulates iodide in its pharynx, and stores it mostly as iodide.
2. When the sodium chloride concentration of the ambient sea water is raised, the amount of iodide accumulated is increased, and traces of a ‘thyronine’ can be detected.
3. When the osmotic pressure was raised with sucrose (instead of NaCl) there was no increased uptake of iodine.