STRETCH RECEPTOR ORGANS IN SQUILLA MANTIS LATR. (CRUSTACEA: STOMATOPODA).

Abstract

ABSTRACT Structures which have been described as muscle receptor organs were found to respond to experimentally applied stretch. The presence of both slowly-adapting and fast-adapting receptors was determined in those organs where two sensory cells and two receptor muscles have been described, i.e. in the abdomen and posterior four thoracic segments. In the fourth thoracic segment, with two cells on a single receptor muscle, one organ is slowly-adapting and the other fast-adapting, with properties not distinguishable from those where separate receptor muscles are present. In the third thoracic segment, with a single cell and receptor muscle, the organ is slowly-adapting. In the second thoracic segment a slowly-adapting cell was discovered. It is without a receptor muscle or accessory innervation and resembles an N-cell of the Decapoda. The reactions of the abdominal organs to acetylcholine and to y-amino butyric acid are qualitatively similar to those in Decapoda. The series of stretch-sensitive organs in Squilla and in Decapoda are compared. The evidence supports the hypothesis that there was, in the trunk of the primitive Malacostraca, a segmentally arranged series of slowly-adapting and fast-adapting receptor organs, that anatomical simplification of the anterior organs has occurred progressively with the development of the carapace and that N-cells are derived from the slowly-adapting type.