Homostrophic Reflex and Stereotropism in Diplopods

1. With suitable arthropods, such as the diplopods, it can be shown that body orientation following passive unilateral tension involves the homostrophic reflex. The phenomenon is exhibited when the animal is quiescent and during forward locomotion, but nothing of the sort appears in backward locomotion. 2. Receptors for the homostrophic reflex are in the body wall and are distributed throughout the length of the animal. 3. The effector nerves take their origin from the ganglia of the head alone. 4. The diplopods are stereotropic, the head turning toward the side in contact with a solid surface only as long as some part of the body maintains contact. Under suitable conditions stereotropism may mask the homostrophic reflex. 5. When a diplopod is in contact with two lateral surfaces of equal extent the path upon emergence is a straight one, conforming to the law of the parallelogram of forces.