Variations in histology of abdominal stretch receptors of saturniid moths during development

Abstract

ABSTRACT In the stretch receptors of Lepidoptera there are normally two giant nuclei, but supernumerary giant nuclei are frequently present. In a study on Sarnia cynthia supernumerary giant nuclei have been found to occur most frequently in the first, second, third, and fourth abdominal segments. They are present in the larva, pupa, and adult. Small nuclei in the muscular component of the receptors are infrequent in the larva and in the fourth, fifth, and sixth abdominal segments of the adult; but in the first, second, and third abdominal segments there is an increase in small nuclei at metamorphosis. Small nuclei also multiply in the receptors of the eighth and ninth segments but these receptors degenerate. The muscular component of the receptors that metamorphose at first becomes reduced and loses its striations and then differentiates anew. In those receptors that disappear (eighth and ninth) dedifferentiation is succeeded by histolysis. A third category of nucleus, larger than the small nuclei but smaller than the giant nuclei, was found in a few receptors of larva, pupa, and adult. Such nuclei appear to be absent from the fifth and sixth segments, but they were too rare for reliable statistics to be obtained.