1. A single stimulus to each of the walking legs and chelae of the anomuran, Petrolisthes armatus, was found to cause, in most animals, the autotomy of four or more of these eight appendages. The appendages least often dropped were the first, sixth, seventh, and eighth of a series, when the order of stimulation was a random one. A regular increasing tendency to autotomize in the first four legs was followed by a decreasing tendency in the remainder.2. Injection of acetylcholine in relatively high concentrations caused the autotomy of one to several legs without further stimulation. A concentration was found which only occasionally caused autotomy when injected, but which facilitated the autotomy of the first three legs to be stimulated and eliminated, thereby, the period of increasing tendency to autotomize.3. The injection of eserine caused a marked increase in general activity and a relatively small amount (0.1 gamma per animal) facilitated the autotomy of the first and second legs. The injection of ese...