Changes in internal pressure during puparium formation in flies

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Abstract
Changes in the internal pressure of fly larvae during puparium formation were measured by a method previously described. Two different types of pressure changes were recorded: (1) Reversible pulsations of various types corresponding to different kinds of muscular contractions, and (2) an irreversible increase of the pressure baseline caused by dimensional shrinkage and loss of elasticity of the cuticle, association with ultrastructural reorganization and sclerotization. The pressure pulses potentiated by neuromuscular activity are association with the initial stages of pupariation, immobilization, retraction of the anterior segments, and longitudinal body contraction, and can generate pressure peaks of up to 300 mm Hg. By contrast, the steady rise of the basic pressure during the final stages of pupariation is generated independently of muscular activity and is also independent of phenolic tanning. The basic pressure can reach levels of 100 mm Hg and is indispensable for the final rounding and smoothening of the ovoid puparium. Morphogenesis of the puparium thus can be understood as a result of a delicate concert between neuromuscular activity and structural changes in the integument.