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The chemical composition of pupating insects has been frequently studied ever since the time of Claude Bernard. The earlier work has been adequately reviewed by Needham (1931). Among the more recent investigations may be mentioned those of Ludwig (1932) and Crescitelli and Taylor (1935). Since the blowfly laboratory here at the Ohio State University is able to furnish almost unlimited amounts of material, the investigations of the changes in the chemical composition of Phormia regina which are reported in this paper have been carried out more completely and on a much larger scale than any previously reported. We have determined total water, ash, nitrogen, fats and carbohydrate (reducing substance) and non-protein nitrogen in the larvae, at 24 hour intervals during the four days of pupation, in the adults, and in the pupal cases, and have measured the rate of weight loss during pupation.

In a system such as the pupating insect the interconversion of foodstuffs can perhaps be best studied by comparison of the bodilycomposition of the organism at various stages of its metamorphosis. In our work we have attacked this problem in two ways; first, by calculation of the composition from the combustion respiratory quotient as determined in the oxycalorimeter; and second, by conventional chemical analysis. The results obtained by the first of these methods are reported in this paper.

The physiology of pupation is of importance not only from the comparative point of view but also from the standpoint of general physiology. The pupating insect is excellent material for the study of the transformation of foodstuffs, since in this process there is a complete reorganization of body tissues while the only exchange between the organism and its environment is gaseous. There have been a number of studies on the subject, among which may be mentioned the work of Frew (1929), Taylor and Steinbach (1931), and Crescitelli (1935). Reviews of the older work are contained in the papers of Needham (1929, 1931) and Hoskins and Craig (1935). However the literature contains little or nothing on the common blowfly ( Phormia regina ).