CHEMICAL MEDIATION IN CRUSTACEANS. III. ACETYL-CHOLINE AND AUTOTOMY IN PETROLISTHES ARMATUS (GIBBES)

Abstract

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 eserine never caused legs to be dropped unless they were stimulated, otherwise its effects on autotomy were very similar to those produced by acetylcholine. 4. Atropine caused a general lowering of excitability and in relatively high concentrations completely prevented autotomy. 5. The injection of adrenalin was followed by a reduction in the percentage of autotomies of each of the eight legs but the phases of increasing and decreasing "excitability" remained unchanged. 6. No differences, correlated with sex or the bearing of eggs, were found in the average number of autotomies per individual. 7. The evidence obtained has been interpreted as indicating that acetyicholine normally plays a rôle in the autotomy reflex of Petrolisthes probably by acting as a mediator of impulses between the motor nerve and autotomizer muscle of a leg.