The extent of air in the tracheoles of some terrestrial insects

Abstract

Abstract Recently a theory was put forward (Wigglesworth, 1930) according to which the extent of air in the tracheal of insects is determined by the osmotic pressure of the tissue fluids in which these capillaries are bathed. Thus, whereas in a state of rest the terminal region of the tracheoles contains fluid, when the tissues are active the consequent increase in osmotic pressure leads to the removal of this theory the removal of fluid would thus have a certain physiological significance in improving the supply of oxygen to the active tissues. These conclusions were based almost solely on experiments on the larva of the mosquito; and in a later paper (Wigglesworth, 1931, a, although it was recognised that osmotic pressure is probably in all cases the force which keeps the tracheæ more or less filled with air, it was suggested that "in terrestrial insects, with a limited supply of water, the osmotic pressure of the tissue fluids may, at times, be far higher than in an aquatic insect like the mosquito larva; and this high osmotic pressure might be expected to draw the fluid into such fine tracheoles that any further increase due to muscular contraction will have no significant effect."