The Thoracic Gland in Rhodnius Prolixus (Hemiptera) and Its Role in Moulting

It is now generally accepted that the periodic phases of growth in insects, which terminate in the deposition of a new cuticle and the casting of the old skin, are initiated by chemical changes in the circulating blood. For these growth-stimulating factors the general term ‘moulting hormone’ has been used (Wigglesworth, 1934), although it has been realized for some time that this hormone ‘might ultimately prove to be made up of more than one constituent’ (Wigglesworth, 1940) and that a succession of secretions might in fact be concerned (Williams, 1947; Wigglesworth, 1949).