The influence of saline media upon the longevity, water content and polysaccharide content ofMoniezia expansais discussed. Worms may live two or three days in balanced salines but in the majority of experiments they die between 9 and 12 hours. Addition of glucose abbreviates the longevity period in saline media. The water content is affected only slightly by balanced salines but is influenced by the concentration of sodium chloride and by the presence of sugars and amino acids; behavior in saline media cannot be correlated wholly with changes in water content. The polysaccharide content is not significantly different from mammalian glycogen, constitutes 0.35 to 5. 25% of the fresh weight, remains stable during immersion of the living worm for six hours in media that reduce muscle tonus, but decreases during immersion in media that encourage muscle tonus. Glycogen increase occurs when the medium contains glucose up to 1%, but not when the glucose content exceeds this amount or when the glucose is replaced by other sugars, by amino acids, or by glycoproteins. Saline media are adjudged unfavorable to tapeworm existencein vitro.