Observations on Difflugia pyriformis and D. acuminata yielded essentially the same results. Locomotion is normally brought about by the extension of pseudopods, one after another, and attachment to the substratum at the tip, followed by contraction which pulls the shell containing the body forward. Movement is consequently intermittent. The extension of pseudopods in Difflugia is in principle the same as in Amoeba proteus, and contraction is probably also the same in principle, but it is much more pronounced and much more highly specialized in Difflugia than in Amoeba, in which it does not function appreciably in the process of locomotion. The pseudopods in Difflugia after they are extended wave about considerably, doubtless owing to unequal local contraction of the plasmagel on opposite sides. Weak local contact stimulation of an extended pseudopod causes sharp bending in this region toward the side stimulated. Strong general contact stimulation causes rapid contraction of the entire pseu dopod. The bending is due to local thickening of the plasmagel in the region stimulated. Contraction of the entire pseudopod is due to thickening of the piasmagel in the entire pseudopod. Contact stimulation results, under certain conditions, in gelation which extends far beyond the region stimulated. There is therefore in Difflugia transmission of something akin to an impulse in higher forms. If the shell is broken, Difflugia leaves it, moves about freely and lives for a week or more. The process of locomotion, under such conditions, is in all respects like that in Amoeba. Contraction of pseudo-pods, so conspicuous in specimens containing shells, is practically absent.