Microanatomy of T H E Abdominal Stretch Receptors of T H E Crayfish (astacus Fluviatilis L.) by Elisabeth Florey* and Ernst Florey*~

Since Alexaudrowicz (1951) first described muscle receptor organs in the abdomen of Ho~m~rus ~garis and P~linurus ~ulgaris, several authors have studied the physiological and pharmacological properties of such organs, using mainly various species of crayfish as their objects of study. These investigations were based mainly upon the histological evidence presented by Alexandrowicz, concerning the microanatomy of the muscle receptor organs of lobsters (tto~rus and Pa2inurus, belonging to the families of Homaridae and Palinuridae). A study of the microanatomy of the muscle receptor organs (stretch receptors) of a representative species of crayfish (family of Astacidae) seemed to us interesting and necessary. We have found important differences between the microanatomy of the stretch receptors of Astacus and that described by Alexandrowicz (1951) for Homarus and Palinurus, differences which are of special interest with respect to the recent analysis of the stretch receptor physiology by Kufller and Eyzaguirre. In addition some general features of the receptor neurons have been noted which have not been described previously. Method The abdominal stretch receptors were dissected from large specimens of Astacus fluvia~ilis L. Males were used exclusively and the receptors have been taken from the second and third abdominal segments. The method of dissection has been principally that described by Wiersma, Furshpan, and Florey (1953). The receptor musdes and the supplying nerve were mounted in their original orientation on a small glass frame (4 X 4 ram.) by means of a fine nylon thread (10# in diameter). When lifted out of any solution the frame carried a film of fluid thus protecting the extremely delicate structure of the receptors from damage when it had to pass through the surface into another solution. Methylene blue has been used in but a few preparations; most of the stretch receptor organs were stained according to the sodium hydroxyde silver method of