ABSTRACT
During development the tracheal system of insects is at first filled with fluid. About the time of hatching from the egg and at each subsequent moult this fluid is absorbed into the tissues. The mechanism of absorption was studied in a number of insects, and earlier work on the subject reviewed, by Sikes & Wigglesworth (1931), who concluded that although secretory activity might be responsible for the presence in the tracheal system of a fluid which could be absorbed by osmosis, the final absorption was probably brought about by the osmotic pressure of the blood. At the suggestion of Prof. A. Krogh, who has taken an active interest throughout this work, the problem has been reinvestigated with a view to differentiating the part played by secretion.
It is probable that much of the fluid occupying the main tracheal trunks is discharged with the old cuticle. Stadtmann-Averfeld (1923) describes this as happening in the first-stage larva after hatching, but that I am unable to confirm.
