Structural changes in the epidermal cells of Rhodnius during tracheole capture.

Epidermal cells deprived of their oxygen supply by tracheal section give off cytoplasmic processes which become attached to air-filled tracheoles in neighbouring areas and draw these into the oxygen-deficient zone. Many of these cytoplasmic strands exceed 100 micrometer in length but may be no more than 50 nm in diameter; they contain mitochondria, ribosomes, microtubules and microfilaments. In basis structure they resemble the tendon cells; and also the tapering conical epidermal cells along the intersegmental borders of the abdomen, the terminal strands of which are inserted into the basement memebrane behind and in front of the segmental boundaries. The cytoplasmic walls of those tracheoles most exposed to tension during the process of tracheole capture become thickened and packed with microtubules. In all these structures the microtubules are believed to be concerned in resistance to tension. Contraction is presumably effected by microfilaments, but no new evidence is given. The possible role of the epidermal strands in the transport of energy-rich metabolites is discussed.