TRACHEAL FILLING IN SCIARA LARVAE

¹ Laboratory of Physical Biology, National Institutes of Health, Bethesda 14, Maryland

(1) After each molt the new tracheal system of a Sciara larva in air normally remains filled with liquid for 3 to 8 minutes. It then fills spontaneously, rapidly and completely with gas, beginning at some point in a main trunk. The gas comes from some internal source.

(2) Sciara larvae can molt under aerated water, and can fill their tracheal systems with gas while completely submerged in aerated or boiled water, or mineral oil.

(3) Tracheal filling can occur if the larva is in a mixture of 99.7 per cent CO₂, CO or N₂ with 0.3 per cent O₂, but not in complete absence of O₂.

(4) Tracheal filling is indefinitely inhibited near 0° C.

(5) Filling may be stopped and restarted repeatedly by alternating exposures to anoxic gas and air, or to low and room temperatures.

(6) Initiation and progress of tracheal filling are apparently independent of body movements, body hydrostatic pressure, and critical gas ratios.

(7) It is suggested tentatively that tracheal filling involves a metabolic process.

(8) A review and critique of previously proposed mechanisms of tracheal filling is presented.