IS THERE AN ORIENTATION-DEPENDENT EXCURSION OF THE MULLER BODY IN THESTATOCYSTOID OF LOXODES

The ciliate Loxodes possesses a number of vesicles at its anterior dor sal margin. These so-called Muller vesicles contain a spherical inclus ion (Muller body) in which lie crystals of barium salts. The Muller bo dy is connected via a stalk to the wall of its vesicle. It is presumed to function as a stato-organelle and to respond by visible motions to changes of the direction of gravity. We have attempted to document th e motion of the Muller body with respect to the direction of the gravi ty vector. Living cells moving in a horizontal or a vertical plane hav e been viewed under the light microscope with differential interferenc e contrast, documented on video film, and sequences of single frames h ave been evaluated. Apparent excursions of the Muller body by about 1. 5 mu m, corresponding to a deviation of 10 degrees at the base of the stalk, are observed in cells moving in a horizontal plane. No larger e xcursions have been seen in the vertical plane. Implications of this r esult for a model of the stato-organelle are discussed.