CUTANEOUS AND TRACHEAL RESPIRATION IN THE PHORMIA LARVA

¹ Laboratory of Physical Biology, National Institutes of Health, Public Health Service, Department of Health, Education, and Welfare, Bethesda, Maryland

1. In the Phormia regina larva oxygen uptake from air at 25° of larvae with both pairs of spiracles ligated off is about 0.09 µL/mg. live wt./hr. (10% of normal respiration) and increases four-fold in oxygen. This is the maximum cutaneous uptake possible from air.

2. The posterior pair of spiracles by itself can admit enough oxygen from air to supply normal needs.

3. On the basis of reciprocal ligation experiments, the anterior spiracles have about half the "capacity" of the posterior spiracles for admitting oxygen into the tracheal system, and can, by themselves, admit about 60% of normal needs.

4. The internal pO₂ in larvae with both pairs of spiracles ligated is zero, even in an atmosphere of pure oxygen.

5. In normal (non-hypoxic) larvae, cutaneous respiration accounts for less than 2.5% of the total oxygen uptake.

6. The permeability of the integument to oxygen is of the order of 0.005 µL/mm.²/min./atm.

7. DDT does not affect cutaneous permeability to oxygen.

8. DDT-poisoned larvae cannot obtain enough oxygen from air even with all spiracles and skin functional, the hypoxia increasing nonlinearly in the order unligated < anteriorly ligated < posteriorly ligated < doubly ligated. Even in pure oxygen the larvae are hypoxic if either pair of spiracles is cut off.