The Role of the Epidermal Cells in the 'migration' of Tracheoles in Rhodnius Prolixus (hemiptera)

During the moulting process the tracheal system grows by the extension of new tracheae and tracheoles from the existing tubes. Outgrowths are produced by the active movements of the formative cells of the tracheal epithelium; these give out filiform 'amoeboid* processes which move into those regions most deficient in oxygen (Wigglesworth, 1954). Changes in the distribution of the tracheae can take place also in the absence of any growth. If an extensive area of the epidermis in the non-moulting insect is deprived of its oxygen supply by cutting a main trachea, the tracheoles from adjacent regions ' migrate' in to relieve the deficiency. Many attempts were made to discover the mechanism of this movement, in which considerable forces of traction are evidently involved. But none of the ordinary staining methods employed revealed the strands responsible for the tension on the tracheoles; and it was assumed that amoeboid processes from the cytoplasm of the tracheoles were again concerned—although surprise was expressed at the apparent magnitude of the force they were able to exert. It was supposed that the tips of the tracheoles are 'attracted' to regions deficient in oxygen. That seems a reasonable assumption when new tracheal cells containing no air-filled tubes are growing outwards during the moulting process. But the tracheoles (in the Rhodnius epidermis) contain air right up to their extremities; and they carry this air with them as they 'migrate'. This thought suggested the possibility that the force of traction might be exerted, not by the cytoplasm of the tracheole, but by the epidermal cells which are in need of oxygen; and that in the non-growing insect the tracheoles might play only a passive role in the movement. The main object of the present work was to test this possibility.