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Stretch Receptor Organs in the Thorax of the Hermit Crab, Pagurus Bernhardus (L. 1758)

Muscle receptor organs (MRO) are present in the abdomen in a wide variety of higher Crustacea (see review by Alexandrowicz, 1967), though most experimental work on these organs has been carried out on representatives of only the Astacura and Palinura, in which the anatomy is relatively uniform. In the very varied group Anomura, they have been reported from among the Galatheidea, Thalassinidea and Paguridea (Alexandrowicz 1952b; Pilgrim, 1960); in the latter paper, they were shown to have properties physio-logically similar to those of the Astacura and Palinura, with slowly- and fast-adapting components. Stretch sensitive organs also occur in the thorax of many forms, but are of two distinct types there. In the posterior thorax are MRO comparable with those of the abdomen, i.e. comprising receptor cell, specialized muscle and a complex innervation of excitatory and inhibitory nerves as well as sensory fibres. In the more anterior thorax are the relatively very simple N-cells, whose dendrites spread among the fibres of non-specialized muscle and which are not known to possess any accessory innervation (Alexandrowicz, 1952a).