Studies on the initiation of growth and moulting in Locusta migratoria migratorioides R. & F.—III. The role of the frontal ganglion

Abstract

A brief review is given of some of the functions hitherto attributed to the frontal ganglion. An account is given of its gross anatomy and histology. The posterior and anterior pharyngeal nerves have been traced to the surface of the gut. The posterior pharyngeal nerves end on the anterior surface of the pharynx in two groups of three sensory organs dorso-lateral to the midline. Histologically these cells resemble the stretch receptors figured by Finlayson and Lowenstein, and this functions is provisionally accepted for them. Further studies were made on the effect of removal of the frontal ganglion at different times during the instar on the growth and moulting of the locust. Animals in which the frontal ganglion had been removed at 0, 12, and 24 hr showed a slight increase in weight and then remained constant until they died; they showed no sign of new cuticle formation at autopsy. Removal at 33 hr resulted in no increase in weight but at autopsy new cuticle formation was found under the old. The locusts did not attempt to ecdyse. Removal at 72 hr resulted in the loss of weight following the operation not being recovered, whereas at 96 hr the animals lost weight until they died some 61 hr later. In both the latter cases new cuticle under the old was found at autopsy. Those 96 hr old had made some attempt to ecdyse but they were unsuccessful due to wound adhesions. Cutting the frontal connectives had the same effect as the removal of the frontal ganglion. For unknown reasons it was always accompanied with a far higher mortality than the seemingly more severe operation of the removal of the frontal ganglion. Cutting one frontal connective had no adverse effect on the further growth and moulting of the locusts. The separation of the frontal ganglion from the surface of the foregut, which involved the cutting of the anterior and posterior pharyngeal nerves, resulted in the complete cessation of growth and moulting in the locust. Comparisons were made of the oxygen consumption of normal, starved, and frontal ganglionectomized insects. No significant difference was found between the operated and the normal locusts in oxygen consumption expressed as mm 3/mg. Starved insects showed a significant drop in oxygen consumption. In time the oxygen consumption of operated insects remained constant. It is concluded that the frontal ganglion forms a link in the passage of nervous impulses originating from the stretch receptors of the pharynx and passing via the posterior pharyngeal nerves, frontal ganglion, and frontal connectives to the brain where they may influence the medial neurosecretory cells, and possibly also via the recurrent nerve and hypocerebral ganglion to the corpora cardiaca.