Growth and Regeneration in the Tracheal System of an Insect, Rhodnius prolixus (Hemiptera)

The tracheoles in Rhodnius are simple or branched tubes, usually 200–350 μ in length, each formed within a single cell, the nucleus of which lies at about 75 μ from the point of origin. They taper gradually from a diameter of 0·7–0·8 μ to end blindly at about 0·2 μ. Once laid down the tracheoles persist unchanged throughout the life of the insect; unlike the tracheae they do not shed their lining cuticle at moulting (cf. Keister on Sciara). New tracheae and tracheoles arise by the outgrowth of columns of cells from the sides or endings of existing tracheae at the time of moulting. The tips of the tracheoles migrate actively towards regions of deficient oxygenation, drawing the tracheae after them. Movements up to one millimetre have been observed. This is the mechanism by which implanted organs are provided with a tracheal supply in the absence of moulting. The outgrowth of new tracheae and tracheoles is greatly stimulated in regions of deficient oxygenation. This is the mechanism of ‘tracheation’ of implanted organs when moulting takes place. If the insect is reared in reduced concentrations of oxygen, there is an increase in the number of large tracheae developed. This is particularly evident in the wing lobes. The general pattern of wing venation is not affected by this altered tracheal arrangement, but minor changes may occur. These are briefly discussed.