and Marine Biological
T W O FIGURX8
I n specialized tissues such as muscle and nerve, chloride exists, in the main, outside the cellular elements-in the tissue spaces-while potassium appears to be held in high concentration inside the cells. It seems reasonably certain that chloride exists within the tissue spaces as sodium chloride in a concentration nearly equivalent to that of the fluid medium bathing the tissue. Potassium, probably existing in ionic form combined with any of several kinds of organic and inorganic ions which may be present, shows no such simple relationship to the potassium ion concentration of the medium.
Experiments relating to the distribution of these elements, particularly on amphibian material, have been carried out by Fenn and his co-workers and have been summarized by him recently (Fenn et al., '34 and Fenn, '36).
This paper reports preliminary findings on the distribution and physicochemical state of chloride and potassium in the retractor muscles of the sea cucumber, Thyone briareus. * This work was supported by a grant from the Graduate School, University of Minnrsota. 429 'I am indebted to Miss Ethel M. Slider for preparing theee elides.