[165] _Herbert S. Jennings_: “Studies on reactions to stimuli in unicellular organisms. I. Reactions to chemical, osmotic and mechanical stimuli in the ciliate infusoria.” Journal of Physiology, Vol. XXI, 189 F. [166] _Pütter_: “Studien über Thigmotaxis bei Protisten.” Arch. f. Anat. and Physiologie, physiol. Abt. Suppl. 1900. [Illustration: Fig. 42. Interference of galvanotaxis and thigmotaxis in Paramaecium aurelia. The individuals which are thigmotactically attached to slime particles remain at rest while the freely swimming individuals move toward the cathodic pole. ] [Illustration: A B Fig. 43. _Hypotrichous infusoria._ A--Stylonychia. B--Urostyla.] Still more complex and striking is finally the following case of interference between thigmotaxis and galvanotaxis. The hypotrichous infusoria as _Stylonychia_, _Urostyla_, _Oxytricha_, etc., have a marked functional and morphological differentiation of their cilia. They possess a bow-like row of perioral cilia, which sweep in the food; a number of cilia on the ventral surface used for locomotion by which they move about upon objects in the water; a row of border cilia on each side, which, during swimming, contribute the propelling force. The perioral cilia also form the elements which bring about a screw-like movement on the axis. They further possess several cilia, which permit a rebounding of the organism, and finally certain forms have anal cilia, which probably serve as breaks and to steer the organism. (Figure 43.) Their usual mode of locomotion is that of creeping, moving by means of the cilia on the ventral surface. These movements depend upon the positive thigmotaxis of the cilia of locomotion. At the same time there is inhibition of the cilia on the sides. When the infusoria are excitated by a new stimulus, the cilia used for rebounding become active, the body frees itself from its position of attachment and begins to swim, wherein the cilia on the sides, as well as the perioral cilia, act in the manner mentioned above. I have made the striking observation that the hypotrichous infusoria respond differently to the galvanic current, depending on whether they are swimming or in a fixed position. If one places a drop of water with numerous Urostyla on a slide between parallel pieces of fired clay which serve as electrodes, it will be seen, upon the closing of a current, that all of the individuals which are freely swimming and turning in a screw-like manner around their axis, steer immediately toward the cathode, exactly as in the case of the Paramecia. On the other hand, those which are fixed to the bottom of the slide as a result of thigmotaxis, upon closing of the current, make a short turn and assume a position wherein the long axis is at right angles to the direction of the current, and the perioral rim is directed toward the cathode. In this position they move through the field. (Figure 44.) When the current is broken the