Mechanisms of the Crayfish Tail Flick

Abstract

THE escape reaction of the crayfish consists of a rapid backward swimming movement brought about by powerful flexion of the abdomen. In the course of a primarily anatomical re-investigation (as yet unpublished) of the musculature responsible for this flexion in the crayfish Procambarus clarki, it was observed that some 40 percent of the cross-sectional area of the main flexor musculature is contributed by three muscles which both arise and insert largely or entirely dorsal to the intersegmental hinge. These are the central, transverse and dorso-lateral muscles, in the terminology of Daniel¹. The expected “direct” action of such muscles would be extension rather than flexion; that so large a proportion of the flexor musculature is apparently “indirect” in its action was considered to be of a sufficiently general physiological interest to be presented separately from the main body of the work.