AN ANGLE SENSE IN THE ORIENTATION OF A MILLIPEDE

Abstract

1. The millipede, Trigoniulus lumbricinus, when forced to crawl through a corridor containing an abrupt turn, tended to turn upon emergence from the corridor at an angle which was opposite and approximately equal to the angle of the forced turn. 2. The response held for forced angles ranging in size up to at least 120°. For forced turns greater than 60° the amount of reverse turning was less than the amount of forced turning. On a statistical basis the millipedes appeared to be capable of distinguishing 10° differences in the angle of the forced turn. 3. There were highly significant differences in the response patterns of individual millipedes to a graded series of forced angles. 4. The turning tendency was significantly increased following a series of turns in the same direction. 5. The precision and sensitivity of the reverse turning response suggest that it is an important orientation reaction for millipedes. A brief survey of the literature on certain maze-running phenomena, reverse turning and spontaneous alternation, further suggests that the response is a type of kinesthetic orientation which may prove to be widespread in animals.